Oxide sintered material and method of manufacturing the same, sputtering target, and method of manufacturing semiconductor device

ABSTRACT

There are provided an oxide sintered material containing an In 2 O 3  crystal phase, a Zn 4 In 2 O 7  crystal phase and a ZnWO 4  crystal phase, and a method of producing the oxide sintered material. The method includes forming the oxide sintered material by sintering a molded body containing In, W and Zn, and forming the oxide sintered material including placing the molded body at a first constant temperature selected from a temperature range of 500° C. or more and 1000° C. or less for 30 minutes or longer.

TECHNICAL FIELD

The present invention relates to an oxide sintered material and a methodof producing the same, a sputtering target, and a method ofmanufacturing a semiconductor device.

The present application claims the benefit of priority to JapanesePatent Application No. 2016-145633 filed on Jul. 25, 2016, the contentof which are incorporated herein by reference in its entirety.

BACKGROUND ART

Conventionally, an amorphous silicon (a-Si) film has been used mainly asa semiconductor film which functions as a channel layer of asemiconductor device such as a TFT (thin film transistor) in a liquidcrystal display device, a thin film EL (electroluminescence) displaydevice, an organic EL display device or the like.

In recent years, as a material to replace a-Si, attention has beenfocused on a complex oxide containing indium (In), gallium (Ga) and zinc(Zn), in other words, an In—Ga—Zn-based complex oxide (also referred toas “IGZO”). It is expected that such IGZO-based oxide semiconductor willhave a higher carrier mobility than that in a-Si.

For example, Japanese Patent Laying-Open No. 2008-199005 (PTL 1)discloses that an oxide semiconductor film mainly composed of IGZO isformed by a sputtering method using an oxide sintered material as atarget.

Japanese Patent Laying-open No. 2008-192721 (PTL 2) discloses an oxidesintered material containing In and tungsten (W) as a material suitablyused for forming an oxide semiconductor film by a sputtering method orthe like.

Moreover, Japanese Patent Laying-open No. 09-071860 (PTL 3) discloses anoxide sintered material containing In and Zn.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laying-open No. 2008-199005

PTL 2: Japanese Patent Laying-open No. 2008-192721

PTL 3: Japanese Patent Laying-open No. 09-071860

SUMMARY OF INVENTION

According to one embodiment of the present invention, an oxide sinteredmaterial includes an In₂O₃ crystal phase, a Zn₄In₂O₇ crystal phase and aZnWO₄ crystal phase.

According to another embodiment of the present invention, a sputteringtarget includes the oxide sintered material according to theaforementioned embodiment.

According to still another embodiment of the present invention, a methodof manufacturing a semiconductor device including an oxide semiconductorfilm includes preparing a sputtering target according to theaforementioned embodiment, and forming the oxide semiconductor film by asputtering method using the sputtering target.

According to still another embodiment of the present invention, a methodof producing an oxide sintered material according to the aforementionedembodiment includes forming the oxide sintered material by sintering amolded body containing indium, tungsten and zinc. Forming the oxidesintered material includes placing the molded body at a first constanttemperature selected from a temperature range of 500° C. or more and1000° C. or less for 30 minutes or longer.

According to still another embodiment of the present invention, a methodof producing an oxide sintered material according to the aforementionedembodiment includes preparing a primary mixture of a zinc oxide powderand an indium oxide powder, forming a calcined powder by heat-treatingthe primary mixture, preparing a secondary mixture of raw powdersincluding the calcined powder; forming a molded body by molding thesecondary mixture, and forming the oxide sintered material by sinteringthe molded body. Forming the calcined powder includes forming a complexoxide powder including zinc and tungsten as the calcined powder byheat-treating the primary mixture at a temperature of 550° C. or moreand less than 1300° C. in an oxygen-containing atmosphere.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic plan view illustrating an exemplary semiconductordevice according to an embodiment of the present invention;

FIG. 1B is a schematic cross-sectional view taken along a line IB-IBillustrated in FIG. 1A;

FIG. 2 is a schematic cross-sectional view illustrating anotherexemplary semiconductor device according to an embodiment of the presentinvention;

FIG. 3 is a schematic cross-sectional view illustrating still anotherexemplary semiconductor device according to an embodiment of the presentinvention;

FIG. 4A is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIGS. 1Aand 1B;

FIG. 4B is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIGS. 1Aand 1B;

FIG. 4C is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIGS. 1Aand 1B;

FIG. 4D is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIGS. 1Aand 1B;

FIG. 5A is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIG. 2;

FIG. 5B is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIG. 2;

FIG. 5C is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIG. 2;and

FIG. 5D is a schematic cross-sectional view illustrating an exemplarymethod of manufacturing the semiconductor device illustrated in FIG. 2.

DETAILED DESCRIPTION Problem to be Solved by Present Disclosure

As described in PTL 1, the TFT including the IGZO-based oxidesemiconductor film as a channel layer has a problem that thefield-effect mobility thereof is as low as about 10 cm²/Vs.

Although PTL 2 proposes a TFT which includes, as a channel layer, anoxide semiconductor film formed by using an oxide sintered materialcontaining In and W, no investigation has been made on the reliabilityof the TFT.

As described in PTL 3, the thin film formed by using the oxide sinteredmaterial is a transparent conductive film which has a lower electricalresistance than the semiconductor thin film used as a channel layer of aTFT, for example.

In a sputtering method using an oxide sintered material as a sputteringtarget, it is desired to reduce abnormal discharge during sputtering,and it is also desired to use an oxide sintered material which has areduced amount of pores (vacancy) as a sputtering target. Regarding theoxide sintered material described in PTL 3, unless the oxide sinteredmaterial is prepared at a higher sintering temperature, it is impossibleto reduce the amount of pores. However, if the sintering temperature isset to a higher temperature, the time required to raise the temperatureand the time required to lower the temperature will become longer, andmore electric energy will be needed to maintain the sintering atmosphereat a higher temperature, which thereby deteriorates the productivity.Moreover, if the sintering temperature is set to a higher temperature,tungsten oxide included in the raw material may be evaporated, andthereby, the obtained oxide sintered material may contain no W.

Further, according to the invention described in PTL 2, it is impossibleto obtain an oxide sintered material having a high sintered density (theapparent density of the oxide sintered material after sintering), and asa result, the number of pores in the oxide sintered material issignificantly large.

An object of the present invention is to provide an oxide sinteredmaterial containing In, W and Zn, which is capable of reducing abnormaldischarge during sputtering and reducing the amount of pores in theoxide sintered material. Another object is to provide a method ofproducing the oxide sintered material capable of producing the oxidesintered material even at a lower sintering temperature.

Still another object is to provide a sputtering target including theoxide sintered material and a method of manufacturing a semiconductordevice including an oxide semiconductor film formed by using thesputtering target.

Advantageous Effect of the Present Disclosure

According to the description in the above, it is possible to provide anoxide sintered material capable of reducing abnormal discharge duringsputtering and the amount of pores contained therein. Further, accordingto the description in the above, it is possible to provide a methodcapable of producing the oxide sintered material even at a lowersintering temperature.

Description of Embodiments

First, embodiments of the present invention will be enumerated anddescribed hereinafter.

[1] An oxide sintered material according to an embodiment of the presentinvention includes an In₂O₃ crystal phase, a Zn₄In₂O₇ crystal phase, anda ZnWO₄ crystal phase. According to the oxide sintered material, it ispossible to reduce abnormal discharge during sputtering and reduce theamount of pores in the oxide sintered material. The oxide sinteredmaterial according to the present embodiment may be suitably used as asputtering target for forming an oxide semiconductor film (such as anoxide semiconductor film serving as a channel layer) included in asemiconductor device.

[2] In the oxide sintered material according to the present embodiment,a diffraction angle 20 at the X-ray diffraction peak derived from theIn₂O₃ crystal phase is preferably greater than 50.70° and smaller than51.04°, which is advantageous in reducing abnormal discharge duringsputtering.

[3] In the oxide sintered material according to the present embodiment,the content of the In₂O₃ crystal phase is preferably 25 mass % or moreand less than 98 mass % and the content of the Zn₄In₂O₇ crystal phase ispreferably 1 mass % or more and less than 50 mass %, which isadvantageous in reducing abnormal discharge during sputtering and theamount of pores in the oxide sintered material.

[4] In the oxide sintered material according to the present embodiment,the lattice constant of a C-plane of the Zn₄In₂O₇ crystal phase ispreferably 33.53 Å or more and 34.00 Å or less, which is advantageous inreducing abnormal discharge during sputtering.

[5] In the oxide sintered material according to the present embodiment,the content of the ZnWO₄ crystal phase is preferably 0.1 mass % or moreand less than 10 mass %, which is advantageous in reducing abnormaldischarge during sputtering and the amount of pores in the oxidesintered material.

[6] In the oxide sintered material according to the present embodiment,the content of tungsten relative to the total of indium, tungsten andzinc in the oxide sintered material is preferably more than 0.1 atom %and less than 20 atom %, and the content of zinc relative to the totalof indium, tungsten and zinc in the oxide sintered material ispreferably more than 1.2 atom % and less than 40 atom %, which isadvantageous in reducing abnormal discharge during sputtering and theamount of pores in the oxide sintered material.

[7] In the oxide sintered material according to the present embodiment,the content of zinc relative to the content of tungsten in the oxidesintered material is preferably greater than 1 and less than 80 by atomratio, which is advantageous in reducing the amount of pores in theoxide sintered material.

[8] The oxide sintered material according to the present embodiment mayfurther include zirconium (Zr). In this case, the content of zirconiumrelative to the total of indium, tungsten, zinc and zirconium in theoxide sintered material is preferably 0.1 ppm or more and 200 ppm orless by atom ratio, which is advantageous in maintaining a highfield-effect mobility for a semiconductor device manufactured by usingthe oxide sintered material of the present embodiment as a sputteringtarget even if it is annealed at a high temperature.

[9] The sputtering target according to another embodiment of the presentinvention includes the oxide sintered material of the above embodiment.According to the present embodiment, since the sputtering targetincludes the oxide sintered material of the above embodiment, it ispossible to reduce abnormal discharge during sputtering. In addition,according to the sputtering target of the present embodiment, since theamount of pores is reduced, it is possible to provide a semiconductordevice having excellent characteristics such as capable of maintaining ahigh field-effect mobility even if it is annealed at a high temperature.

[10] A method of manufacturing a semiconductor device according to stillanother embodiment of the present invention is a method of manufacturinga semiconductor device including an oxide semiconductor film, the methodincludes preparing a sputtering target according to the aboveembodiment, and forming the oxide semiconductor film by a sputteringmethod using the sputtering target. According to the manufacturingmethod of the present embodiment, since the oxide semiconductor film isformed by the sputtering method using the sputtering target of the aboveembodiment, it is possible for the semiconductor device to exhibitexcellent characteristics such as capable of maintaining a highfield-effect mobility even if it is annealed at a high temperature. Thesemiconductor device is not particularly limited, and as a preferableexample, a TFT (thin film transistor) which includes, as a channellayer, an oxide semiconductor film formed by a sputtering method usingthe sputtering target of the above embodiment may be given.

[11] A method of manufacturing an oxide sintered material according tostill another embodiment of the present invention is the method ofmanufacturing the oxide sintered material of the above embodiment, themethod includes forming the oxide sintered material by sintering amolded body containing indium, tungsten and zinc. Forming the oxidesintered material includes placing the molded body at a first constanttemperature selected from a temperature range of 500° C. or more and1000° C. or less for 30 minutes or longer, which is advantageous inproducing the oxide sintered material of the above embodimentefficiently.

[12] In the method of producing an oxide sintered material according tothe above embodiment in the above [11], forming the oxide sinteredmaterial includes placing the molded body at the first temperature for30 minutes or longer, and placing the molded body in anoxygen-containing atmosphere at a second temperature which is 800° C. ormore and less than 1200° C. and higher than the first temperature inthis order, which is advantageous in reducing the amount of pores in theoxide sintered material to be obtained.

[13] A method of manufacturing an oxide sintered material according tostill another embodiment of the present invention is a method ofmanufacturing an oxide sintered material of the above embodiment, themethod includes preparing a primary mixture of a zinc oxide powder andan indium oxide powder, forming a calcined powder by heat-treating theprimary mixture, preparing a secondary mixture of raw powders includingthe calcined powder, forming a molded body by molding the secondarymixture, and forming the oxide sintered material by sintering the moldedbody, forming the calcined powder including forming a complex oxidepowder including zinc and tungsten as the calcined powder byheat-treating the primary mixture at a temperature of 550° C. or moreand less than 1300° C. in an oxygen-containing atmosphere, which isadvantageous in producing the oxide sintered material of the aboveembodiment efficiently.

[14] In the method of producing an oxide sintered material according tothe above embodiment in the above [13], forming the oxide sinteredmaterial includes placing the molded body at a first constanttemperature selected from a temperature range of 500° C. or more and1000° C. or less for 30 minutes or longer, which is advantageous inproducing the oxide sintered material of the above embodimentefficiently.

[15] In the method of producing an oxide sintered material according tothe above embodiment in the above [14], forming the oxide sinteredmaterial includes placing the molded body at the first temperature for30 minutes or longer, and placing the molded body in anoxygen-containing atmosphere at a second temperature which is selectedfrom a temperature range of 800° C. or more and less than 1200° C. andhigher than the first temperature in this order, which is advantageousin reducing the amount of pores in the oxide sintered material to beobtained.

Details of Embodiments Embodiment 1: Oxide Sintered Material

The oxide sintered material according to the present embodiment containsIn, W and Zn as metal elements, and includes an In₂O₃ crystal phase, aZn₄In₂O₇ crystal phase and a ZnWO₄ crystal phase. According to the oxidesintered material, it is possible to reduce abnormal discharge duringsputtering and the amount of pores in the oxide sintered material.

In the present specification, the term of “In₂O₃ crystal phase” refersto a crystal of an indium oxide mainly containing In and oxygen (O).More specifically, the In₂O₃ crystal phase is a bixbyite type crystalphase having a crystal structure defined in JCPDS (Joint Committee forPowder Diffraction Standards) card 6-0416, and is also called as rareearth oxide C-type phase (or C-rare earth structure phase). As long asthe In₂O₃ crystal phase exhibits the above crystal system, the latticeconstant thereof may vary due to the deficiency of oxygen, or thesolid-dissolution of or the deficiency of element In and/or element Wand/or element Zn or the solid-dissolution of other metal elements.

In the present specification, the term of “ZnWO₄ crystal phase” refersto a crystal of a complex oxide mainly containing Zn, W and O. Morespecifically, the ZnWO₄ crystal phase is a zinc tungstate compoundcrystal phase having a crystal structure represented by a space group ofP12/c1(13) and having a crystal structure defined in JCPDS card01-088-0251. As long as the ZnWO₄ crystal phase exhibits the abovecrystal system, the lattice constant thereof may vary due to thedeficiency of oxygen, or the solid-dissolution of or the deficiency ofelement In and/or element W and/or element Zn or the solid-dissolutionof other metal elements.

In the present specification, the “Zn₄In₂O₇ crystal phase” refers to acrystal of a complex oxide mainly containing Zn, In and O. Morespecifically, the Zn₄In₂O₇ crystal phase is a crystal phase having alaminated structure called a homologous structure, and has a crystalstructure represented by a space group P63/mmc (194) and a crystalstructure defined by JCPDS card 00-020-1438. As long as the Zn₄In₂O₇crystal phase exhibits the above crystal system, the lattice constantthereof may vary due to the deficiency of oxygen, or thesolid-dissolution of or the deficiency of element In and/or element Wand/or element Zn or the solid-dissolution of other metal elements.

Each of the crystal phases mentioned above may be identified by X-raydiffraction. In other words, the presence of all of the In₂O₃ crystalphase, the Zn₄In₂O₇ crystal phase and the ZnWO₄ crystal in the oxidesintered material according to the present embodiment may be confirmedby the X-ray diffraction. Moreover, the X-ray diffraction may be used tomeasure the lattice constant of the Zn₄In₂O₇ crystal phase and the planespacing of the In₂O₃ crystal phase.

The X-ray diffraction may be measured under the following conditions orequivalent conditions.

(Measurement Conditions for X-Ray Diffraction)

θ-2θ method,

X-ray source: Cu Kα ray,

X-ray tube voltage: 45 kV,

X-ray tube current: 40 mA,

Step width: 0.02°,

Step time: 1 second/step,

Measurement range 2θ:10° to 80°.

According to the oxide sintered material according to the presentembodiment containing the In₂O₃ crystal phase and the Zn₄In₂O₇ crystalphase, it is possible to reduce abnormal discharge during sputtering.The possible reason may be that the electric resistance of the Zn₄In₂O₇crystal phase is smaller than that of the In₂O₃ crystal phase. In orderto reduce abnormal discharge during sputtering, the total content of theIn₂O₃ crystal phase and the Zn₄In₂O₇ crystal phase in the oxide sinteredmaterial is preferably 80 mass % or more, and more preferably 85 mass %or more.

According to the oxide sintered material according to the presentembodiment containing the In₂O₃ crystal phase and the Zn₄In₂O₇ crystalphase, it is possible to reduce the amount of pores in the oxidesintered material. The possible reason may be that the ZnWO₄ crystalphase plays the role of promoting sintering during the sintering step.

In the oxide sintered material, the diffraction angle 2θ at the X-raydiffraction peak derived from the In₂O₃ crystal phase is preferablygreater than 50.70° and smaller than 51.04°, which is advantageous inreducing abnormal discharge during sputtering. The diffraction peak isattributed to the (440) plane of the In₂O₃ crystal phase.

If an element is solid-dissolved in or an element is deficient in atleast a part of the In₂O₃ crystal phase, the plane spacing may becomewider or narrower than the plane spacing defined in JCPDS card 6-0416.In the JCPDS card 6-0416, the diffraction peak attributed to the (440)plane of the In₂O₃ crystal phase is at a position where the diffractionangle 2θ is 51.04°, and the plane spacing of the (440) plane is 1.788 Å.

In other words, the X-ray diffraction peak attributed to the (440) planeof the oxide sintered material according to the present embodiment ispreferably located at the lower angle side than the X-ray diffractionpeak attributed to the (440) plane of the In₂O₃ crystal phase defined bythe JCPDS card 6-0416, and has a smaller diffraction angle 20 and alarger plane spacing.

As an example of elements that may be solid-dissolved in at least a partof the In₂O₃ crystal phase, at least one element selected from Zn, W, O,and Zr may be given.

As an example of elements that may cause element deficiency, at leastone element selected from In and O may be given. The solid solution ofelements or the deficiency of elements in the In₂O₃ crystal isadvantageous in reducing the amount of pores in the oxide sinteredmaterial. In other words, the solid solution of elements or thedeficiency of elements may promote the diffusion of elements during thesintering step.

Thereby, the elements may move together with each other during thesintering step, which makes it possible to reduce the pores in the oxidesintered material. Further, the solid solution of elements or thedeficiency of elements in the In₂O₃ crystal phase constituting the oxidesintered material is effective in decreasing the electric resistance ofthe In₂O₃ crystal phase, and thereby is advantageous in reducingabnormal discharge during sputtering.

In order to reduce the amount of pores in the oxide sintered materialand abnormal discharge during sputtering, the diffraction angle 20 atthe X-ray diffraction peak derived from the In₂O₃ crystal phase ispreferably greater than 50.80°, and more preferably greater than 50.90°.

In the oxide sintered material, the content of the In₂O₃ crystal phaseis preferably 25 mass % or more and less than 98 mass %, and the contentof the Zn₄In₂O₇ crystal phase is preferably 1 mass % or more and lessthan 50 mass %, which is advantageous in reducing abnormal dischargeduring sputtering and the amount of pores in the oxide sinteredmaterial. The content of the In₂O₃ crystal phase refers to a ratio (mass%) of the In₂O₃ crystal phase when the total amount of the crystalphases detected by X-ray diffraction measurement described below is setto 100 mass %. The same applies to the other crystal phases.

When the content of the In₂O₃ crystal phase is 25 mass % or more, it isadvantageous in reducing abnormal discharge during sputtering, and whenthe content of the In₂O₃ crystal phase is less than 98 mass %, it isadvantageous in reducing the amount of pores in the oxide sinteredmaterial.

In order to reduce abnormal discharge during sputtering and the amountof pores in the oxide sintered material, the content of the In₂O₃crystal phase is more preferably 70 mass % or more and 95 mass % orless, and further preferably 75 mass % or more and 90 mass % or less.

When the content of the Zn₄In₂O₇ crystal phase is 1 mass % or more, itis advantageous in reducing abnormal discharge during sputtering, andwhen the content of the Zn₄In₂O₇ crystal phase is less than 50 mass %,it is advantageous in reducing the amount of pores in the oxide sinteredmaterial.

In order to reduce abnormal discharge during sputtering and the amountof pores in the oxide sintered material, the content of the Zn₄In₂O₇crystal phase is more preferably 5 mass % or more and 30 mass % or less,and further preferably 9 mass % or more and 20 mass % or less.

The Zn₄In₂O₇ crystal phase grows into a spindle shape in the sinteringstep, and thereby, it is present in the oxide sintered material asspindle-shaped particles. The aggregate of spindle-shaped particlestends to generate more pores in the oxide sintered material than theaggregate of circular particles. Therefore, the content of Zn₄In₂O₇crystal phase is preferably less than 50 mass %. On the other hand, ifthe content of the Zn₄In₂O₇ crystal phase is too small, the electricalresistance of the oxide sintered material increases, causing the arcingfrequency to increase during sputtering. Thus, the content of theZn₄In₂O₇ crystal phase is preferably 1 mass % or more.

The content of each crystal phase in the oxide sintered material may becalculated by a RIR method (Reference Intensity Ratio) using X-raydiffraction. Generally, the RIR method quantifies the content based onthe integral intensity ratio of the strongest line of each crystal phaseand the RIR value described in the ICDD card, but in the case of acomplex oxide such as the oxide sintered material according to thepresent embodiment which is difficult to separate the peak of thestrongest line, firstly, the X-ray diffraction peaks clearly separatedfor each compound are selected, and then the content of each crystalphase is calculated from the integrated intensity ratio and the RIRvalue (or by an equivalent method). The measurement conditions of X-raydiffraction performed in determining the content of each crystal phaseare the same as or equivalent to the above-mentioned measurementconditions.

In the oxide sintered material, the lattice constant of the C-plane ofthe Zn₄In₂O₇ crystal phase is preferably 33.53 Å or more and 34.00 Å orless, which is advantageous in reducing abnormal discharge duringsputtering. In order to reduce abnormal discharge during sputtering, thelattice constant of the C-plane of the Zn₄In₂O₇ crystal phase is morepreferably 33.53 Å or more and 34 Å or less, and further preferably33.54 Å or more and 33.59 Å or less.

The lattice constant of the C-plane of the Zn₄In₂O₇ crystal phase iscalculated by using X-ray diffraction. Measurement conditions of X-raydiffraction are the same as or equivalent to the above-mentionedmeasurement conditions. When measured under the above-mentionedconditions, the diffraction peak from the C-plane of the Zn₄In₂O₇crystal phase may appear in the range of 20=31.5° or more and less than32.8°. The lattice constant of the C-plane of the Zn₄In₂O₇ crystal phaseis 33.52 Å when it has a crystal structure defined by the JCPDS card00-020-1438, but the lattice constant of the C-plane of the Zn₄In₂O₇crystal phase contained in the oxide sintered material according to thepresent embodiment is greater than 33.52 Å, and is preferably 33.53 Å ormore and 34.00 Å or less. The Zn₄In₂O₇ crystal phase having such alattice constant is advantageous in reducing abnormal discharge duringsputtering.

The lattice constant of 33.53 Å or more and 34.00 Å or less may beachieved, for example, by solid-dissolving element In and/or element Wand/or element Zn and/or another metal elements in the Zn₄In₂O₇ crystalphase. Due to the solid solution of these elements, the electricalresistance of the Zn₄In₂O₇ crystal phase is lowered, and accordingly,the electrical resistance of the oxide sintered material is lowered,which makes it possible to reduce abnormal discharge during sputtering.

In the oxide sintered material, the content of the ZnWO₄ crystal phaseis preferably 0.1 mass % or more and less than 10 mass %, which isadvantageous in reducing abnormal discharge during sputtering and theamount of pores in the oxide sintered material. The content of ZnWO₄crystal phase is more preferably 0.5 mass % or more and furtherpreferably 0.9 mass % or more so as to reduce the amount of pores in theoxide sintered material, and is more preferably 5.0 mass % or less andfurther preferably 2.0 mass % or less so as to reduce abnormal dischargeduring sputtering.

The content of the ZnWO₄ crystal phase may be calculated by theabove-mentioned MR method using X-ray diffraction. It is found that theZnWO₄ crystal phase has a higher electrical resistivity than the In₂O₃crystal phase and the Zn₄In₂O₇ crystal phase. Therefore, if the contentof the ZnWO₄ crystal phase in the oxide sintered material is too high,abnormal discharge may occur in the ZnWO₄ crystal phase duringsputtering. On the other hand, if the content of ZnWO₄ crystal phase isless than 0.1 mass %, the sintering in the sintering step will not bepromoted, resulting a greater number of pores in the sintered material.

In the oxide sintered material, the content of W (hereinafter alsoreferred to as “W content”) relative to the total of In, W and Zn in theoxide sintered material is more than 0.1 atom % and less than 20 atom %,and the content of Zn (hereinafter also referred to as “Zn content”)relative to the total of In, W and Zn in the oxide sintered material ispreferably more than 1.2 atom % and less than 40 atom %, which isadvantageous in reducing abnormal discharge during sputtering and theamount of pores in the oxide sintered material.

The W content is more preferably 0.3 atom % or more and furtherpreferably 0.6 atom % or more so as to reduce the amount of pores in theoxide sintered material, and is more preferably 15 atom % or less,further preferably 5 atom % or less and further preferably 2 atom % orless so as to reduce abnormal discharge during sputtering.

Making the W content more than 0.1 atom % is advantageous in reducingthe amount of pores in the oxide sintered material. As described above,it is considered that the ZnWO₄ crystal phase plays the role of anauxiliary agent for promoting sintering in the sintering step.Therefore, it is desirable that the ZnWO₄ crystal phase is generatedwith high dispersion during sintering so as to obtain an oxide sinteredmaterial with a small amount of pores. In the sintering step, if theelement Zn and the element W are brought into contact with each otherefficiently, the reaction will be promoted, which makes it possible toform the ZnWO₄ crystal phase. Therefore, if the W content in thesintered material is made more than 0.1 atom %, the element Zn and theelement W may be brought into contact with each other efficiently. Ifthe W content is 0.1 atom % or less, switching driving can not beconfirmed in a semiconductor device including an oxide semiconductorfilm formed by a sputtering method using the oxide sintered material asa sputtering target. The possible reason may be that the electricresistance of the oxide semiconductor film is too low. If the

W content is 20 atom % or more, the content of the ZnWO₄ crystal phasein the oxide sintered material becomes relatively too large, it isimpossible to suppress abnormal discharge starting from the ZnWO₄crystal phase, which makes it difficult to reduce abnormal dischargeduring sputtering.

In order to reduce the amount of pores in the oxide sintered material,the Zn content is more preferably 2.0 atom % or more and less than 30atom %, further preferably more than 5.0 atom % and less than 20 atom %,and even more preferably more than 10.0 atom % and less than 18 atom %.

The Zn content is preferably more than 1.2 atom % and less than 40 atom% so as to reduce the amount of pores in the oxide sintered material. Ifthe Zn content is 1.2 atom % or less, it would be difficult to reducethe amount of pores in the oxide sintered material. If the Zn content is40 atom % or more, the content of the Zn₄In₂O₇ crystal phase in theoxide sintered material becomes relatively too large, it would bedifficult to reduce the amount of pores in the oxide sintered material.

The Zn content has an effect of maintaining a high field-effect mobilityfor a semiconductor device including an oxide semiconductor film formedby a sputtering method using the oxide sintered material as a sputteringtarget even if it is annealed at a high temperature. Therefore, the Zncontent is more preferably 2.0 atom % or more, further preferably morethan 5.0 atom %, and even more preferably more than 10.0 atom %.

The contents of In, Zn and W in the oxide sintered material may bemeasured by ICP emission spectrometry. The Zn content means the amountof Zn/(the amount of In+the amount of Zn+the amount of W) expressed interms of percentage, and the W content means the amount of W/(the amountof In+the amount of Zn+the amount of W) expressed in terms ofpercentage. Each amount is expressed by the number of atoms.

The Zn content relative to the W content in the oxide sintered material(hereinafter also referred to as “Zn/W ratio”) is preferably greaterthan 1 and less than 80 by atom ratio, which is advantageous in reducingthe amount of pores in the oxide sintered material or reducing abnormaldischarge. In order to reduce the amount of pores, the Zn/W ratio ismore preferably greater than 10 and less than 60, and further preferablygreater than 15 and less than 40.

As described above, it is considered that the ZnWO₄ crystal phase playsthe role of an auxiliary agent for promoting sintering in the sinteringstep. Therefore, it is desirable that the ZnWO₄ crystal phase isgenerated with high dispersion during sintering so as to obtain an oxidesintered material with a small amount of pores. In the sintering step,if the element Zn and the element W are brought into contact with eachother efficiently, the reaction will be promoted, which makes itpossible to form the ZnWO₄ crystal phase.

In order to generate a highly dispersed ZnWO₄ crystal phase during thesintering step, it is desirable that the element Zn is present at alarger amount than the element W. Therefore, the Zn/W ratio ispreferably greater than 1. If the Zn/W ratio is 1 or less, the ZnWO₄crystal phase may not be generated with high dispersion during thesintering step, which makes it difficult to reduce the amount of pores.Furthermore, if the Zn/W ratio is 1 or less, Zn preferentially reactswith W during the sintering step to form the ZnWO₄ crystal phase, sothat the amount of Zn for forming the Zn₄In₂O₇ crystal phase isdeficient, and as a result, the Zn₄In₂O₇ crystal phase is less likely tobe formed in the oxide sintered material, the electrical resistance ofthe oxide sintered material increases, causing the arcing frequency toincrease during sputtering. However, if the Zn/W ratio is 80 or more,the content of the Zn₄In₂O₇ crystal phase in the oxide sintered materialbecomes relatively too large, it would be difficult to reduce the amountof pores in the oxide sintered material.

The oxide sintered material may further include zirconium (Zr). In thiscase, the content of Zr (hereinafter also referred to as “Zr content”)relative to the total of In, W, Zn and Zr in the oxide sintered materialis preferably 0.1 ppm or more and 200 ppm or less by atom ratio, whichis advantageous in maintaining a high field-effect mobility for asemiconductor device manufactured by using the oxide sintered materialas a sputtering target even if it is annealed at a high temperature.

In order to maintain a high field-effect mobility for a semiconductordevice even if it is annealed at a high temperature, the Zr content ismore preferably 0.5 ppm or more and less than 100 ppm, and furtherpreferably 2 ppm or more and less than 50 ppm.

The Zr content in the oxide sintered material may be measured by ICPemission spectrometry. The Zr content means the amount of Zr/(the amountof In+the amount of Zn+the amount of W+the amount of Zr), which isexpressed in terms of parts per million. Each amount is expressed by thenumber of atoms.

Embodiment 2: Method of Producing Oxide Sintered Material

In order to efficiently producing the oxide sintered material accordingto Embodiment 1, it is preferable for the method of producing the oxidesintered material to satisfy one or more of the following conditions (1)to (3), it is more preferable for it to satisfy 2 or more conditions,and it is further preferable for it to satisfy all of the 3 conditions.

condition (1): including a step of forming the oxide sintered materialby sintering a molded body containing indium, tungsten and zinc, and thestep of forming the oxide sintered material includes placing the moldedbody at a first constant temperature selected from a temperature rangeof 500° C. or more and 1000° C. or less for 30 minutes or longer;

condition (2): including a step of forming the oxide sintered materialby sintering a molded body containing indium, tungsten and zinc, and thestep of forming the oxide sintered material includes placing the moldedbody at the first temperature for 30 minutes or longer, and placing themolded body in an oxygen-containing atmosphere at a second temperaturewhich is preferably 800° C. or more and less than 1200° C. and higherthan the first temperature in this order;

condition (3): including a step of preparing a primary mixture of a zincoxide powder and an indium oxide powder; a step of forming a calcinedpowder by heat-treating the primary mixture; preparing a secondarymixture of raw powders including the calcined powder; a step of forminga molded body by molding the secondary mixture; and a step of formingthe oxide sintered material by sintering the molded body.

“Placing a molded body at a first constant temperature selected from atemperature range of 500° C. or more and 1000° C. or less” in the aboveconditions (1) and (2) may be, for example, a heating process in thestep of forming the oxide sintered material through sintering (sinteringstep). As described above, in order to obtain an oxide sintered materialwith a small amount of pores, it is preferable to form a highlydispersed ZnWO₄ crystal phase during the sintering step, and thereby,the molded body is placed at the first temperature for 30 minutes orlonger so as to form a highly dispersed ZnWO₄ crystal phase. Moreover,in order to obtain an oxide sintered material capable of reducingabnormal discharge during sputtering, it is preferable to form aZn₄In₂O₇ crystal phase during the sintering step, and thereby, themolded body is placed at the first temperature for 30 minutes or longerso as to form a highly dispersed Zn₄In₂O₇ crystal phase. After the stepof placing the molded body at the first temperature so as to produce ahighly dispersed ZnWO₄ crystal phase, by increasing the heatingtemperature to the maximum temperature of the sintering step so as topromote the sintering, it is possible to obtain an oxide sinteredmaterial which contains the In₂O₃ crystal phase, the Zn₄In₂O₇ crystalphase and the ZnWO₄ crystal phase and has a small amount of pores. Inaddition, by placing the molded body at the first temperature, theamount of W and Zn solid-dissolved in In₂O₃ will be adjusted, whichmakes it possible to modify the ratio of Zn₄In₂O₇ crystal phase andZnWO₄ crystal phase to a desired ratio.

It should be noted that the term of “the first constant temperature” inthe phrase of “the first constant temperature selected from atemperature range of 500° C. or more and 1000° C. or less” is notnecessarily limited to a specific temperature, it may be a temperaturerange with a margin. Specifically, if a specific temperature selectedfrom a temperature range of 500° C. or more and 1000° C. or less isdenoted as T (° C.), the first temperature may be for example T±50° C.,preferably T±20° C., more preferably T±10° C., and further preferablyT±5° C. as long as it is within the temperature range of 500° C. or moreand 1000° C. or less.

The molded body containing In, W and Zn in the above conditions (1) and(2) may be a molded body containing an indium oxide powder, a tungstenoxide powder and a zinc oxide powder which are raw powders of the oxidesintered material. In the method of producing the oxide sinteredmaterial according to the present embodiment, an In₂O₃ powder may beused as the indium oxide powder. As the tungsten oxide powder, an oxidepowder containing at least one crystal phase selected from the groupconsisting of a WO₃ crystal phase, a WO₂ crystal phase and a WO_(2.72)crystal phase may be used. As the zinc oxide powder, a ZnO powder may beused.

“Placing the molded body in an oxygen-containing atmosphere at a secondtemperature which is preferably 800° C. or more and less than 1200° C.and higher than the first temperature” in the above condition (2) is astep of promoting or completing the sintering. The oxygen-containingatmosphere may be air atmosphere, nitrogen-oxygen mixed atmosphere,oxygen atmosphere or the like. The second temperature is more preferably900° C. or more and 1195° C. or less, and further preferably 1100° C. ormore and 1190° C. or less. If the second temperature is 800° C. or more,it is advantageous in reducing the amount of pores in the oxide sinteredmaterial. If the second temperature is less than 1200° C., it isadvantageous in suppressing the deformation of the oxide sinteredmaterial so as to fit it properly to the sputtering target.

In the method satisfying the above condition (3), a calcined powdercomposed of a complex oxide containing Zn and In is formed from a zincoxide powder and an indium oxide powder, and the calcined powder is usedto form a molded body containing indium oxide powder and tungsten oxidepowder and zinc oxide powder, and the molded body is sintered to givethe oxide sintered material.

The calcined powder preferably contains the Zn₄In₂O₇ crystal phase. Inorder to obtain the calcined powder containing the Zn₄In₂O₇ crystalphase, an indium oxide powder such as an In₂O₃ powder and a zinc oxidepowder such as a ZnO powder are mixed so that the molar ratio ofIn₂O₃:ZnO=1:4 to prepare a primary mixture, and the primary mixture isheat-treated in an oxygen-containing atmosphere. The oxygen-containingatmosphere may be air atmosphere, nitrogen-oxygen mixed atmosphere,oxygen atmosphere or the like. The heat treatment temperature ispreferably 550° C. or more and less than 1300° C., and more preferably1200° C. or more.

According to the method including the step of forming a calcined powdercontaining the Zn₄In₂O₇ crystal phase, the step of preparing a secondarymixture by using the calcined powder, and the step of forming a moldedbody by molding the secondary mixture, in the step of forming the oxidesintered material by sintering the molded body (sintering step), if theelement Zn and the element W are brought into contact with each otherefficiently, the reaction will be promoted, which makes it possible toform the ZnWO₄ crystal phase. As described above, it is considered thatthe ZnWO₄ crystal phase plays the role of an auxiliary agent forpromoting sintering. Therefore, if the ZnWO₄ crystal phase is generatedwith high dispersion during sintering, it is possible to obtain an oxidesintered material with a small amount of pores. In other words, if thesintering is performed simultaneously as the ZnWO₄ crystal phase isbeing formed, it is possible to obtain an oxide sintered material with asmall amount of pores.

Further, according to the method including the step of forming acalcined powder containing the Zn₄In₂O₇ crystal phase, the step ofpreparing a secondary mixture by using the calcined powder, and the stepof forming a molded body by molding the secondary mixture, the Zn₄In₂O₇crystal phase tends to remain in the oxide sintered material even afterthe sintering step, which makes it possible to obtain an oxide sinteredmaterial in which the Zn₄In₂O₇ crystal phase is highly dispersed. TheZn₄In₂O₇ crystal phase highly dispersed in the oxide sintered materialcan reduce abnormal discharge during sputtering.

In the step of preparing the secondary mixture after forming thecalcined powder containing the Zn₄In₂O₇ crystal phase, the calcinedpowder may be mixed with the indium oxide powder (for example, In₂O₃powder) and the tungsten oxide powder (for example, an oxide power suchas WO₃ powder containing at least one crystal phase selected from agroup consisting of WO₃ crystal phase, WO₂ crystal phase and WO_(2.72)crystal phase). In preparing the secondary mixture, it is desirable thatthe mixing ratio of the raw powders is adjusted so that the W content,Zn content, Zn/W ratio in the finally obtained oxide sintered materialfall within the above-mentioned preferable ranges, respectively.

For example, it would be difficult to obtain a suitable oxide sinteredmaterial if the oxide sintered material is produced according to any ofthe following methods (i) to (iii):

(i) a method of forming three kinds of powders of the indium oxidepowder, the tungsten oxide powder and the zinc oxide powder, molding andsintering the mixture powder without going through the step of formingthe calcined powder. In this case, since the element Zn and the elementW are not brought into contact with each other efficiently, the reactionwill not be promoted, which makes it difficult to obtain an oxidesintered material with a small amount of pores or an oxide sinteredmaterial containing an In₂O₃ crystal phase, a Zn₄In₂O₇ crystal phase anda ZnWO₄ crystal phase. In addition, since it is difficult to obtain anoxide sintered material containing a Zn₄In₂O₇ crystal phase, it would bedifficult to suppress the occurrence of arcing during sputtering.

(ii) a method of forming a powder containing the ZnWO₄ crystal phase asthe calcined powder, mixing the calcined powder with indium oxide powderand zinc oxide powder, forming a molded body, and sintering the moldedbody. In this case, the

ZnWO₄ crystal phase can not be highly dispersed, which makes itdifficult to obtain an oxide sintered material with a small amount ofpores.

(iii) a method of forming a powder containing the InW₆O₁₂ crystal phaseas the calcined powder, mixing the calcined powder with indium oxidepowder and zinc oxide powder, forming a molded body, and sintering themolded body. Also in this case, it would be difficult to obtain an oxidesintered material with a small amount of pores.

Therefore, in a method of molding and sintering the powder prepared bythe method of mixing three kinds of powders of the indium oxide powder,the tungsten oxide powder and the zinc oxide powder, the method offorming a powder containing the ZnWO₄ crystal phase as the calcinedpowder, and the method of forming a powder containing the InW₆O₁₂crystal phase as the calcined powder so as to obtain the oxide sinteredmaterial according to Embodiment 1, it is preferable to adopt thecondition (1) or (2) described in the above.

Hereinafter, the method of producing the oxide sintered materialaccording to the present embodiment will be described more specifically.In one preferred embodiment, the method of producing an oxide sinteredmaterial is a method of producing an oxide sintered material accordingto Embodiment 1 including a step of preparing a primary mixture of azinc oxide powder and an indium oxide powder; a step of forming acalcined powder by heat-treating the primary mixture; a step ofpreparing a secondary mixture of raw powders including the calcinedpowder; a step of forming a molded body by molding the secondarymixture; and a step of forming the oxide sintered material by sinteringthe molded body, wherein the step of forming the calcined powderincludes forming a complex oxide powder including zinc and tungsten asthe calcined powder by heat-treating the primary mixture at atemperature of 550° C. or more and less than 1300° C. in anoxygen-containing atmosphere.

According to the manufacturing method mentioned above, it is possible toefficiently produce the oxide sintered material according to Embodiment1 which may reduce abnormal discharge during sputtering, has a reducedamount of pores, and may be suitably used as a sputtering target.According to the manufacturing method mentioned above, even at arelatively low sintering temperature, it is possible to produce an oxidesintered material with a reduced amount of pores and capable of reducingabnormal discharge during sputtering. The complex oxide constituting thecalcined powder may be deficient in oxygen or may be subjected to metalsubstitution.

If the heating temperature in the step of forming the calcined powder isless than 550° C., the complex oxide powder containing Zn and In may notbe obtained, and if the heating temperature is 1300° C. or more, theparticle size of the complex oxide powder may become too large to beused suitably. The heating temperature is more preferably 1200° C. ormore.

Further, if a semiconductor device is manufactured by including, as achannel layer, an oxide semiconductor film which is formed by using asputtering target including the oxide sintered material obtained byheat-treating the complex oxide powder containing Zn and In as thecalcined powder, it is possible for it to maintain a high field-effectmobility even if it is annealed at a high temperature.

It is preferable that the complex oxide containing Zn and In furthercontains a Zn₄In₂O₇ crystal phase. Thereby, it is possible to obtain anoxide sintered material capable of reducing abnormal discharge duringsputtering and having a reduced amount of pores. The Zn₄In₂O₇ crystalphase is a complex oxide crystal phase of Zn and In having a crystalstructure represented by a space group P63/mmc (194) and having acrystal structure defined by JCPDS card 00-020-1438. As long as theZn₄In₂O₇ crystal phase exhibits the above crystal system, the latticeconstant thereof may vary due to the deficiency of oxygen and/or thesolid-dissolution of other metal elements. The Zn₄In₂O₇ crystal phasemay be identified by X-ray diffraction.

In order to obtain an oxide sintered material capable of reducingabnormal discharge during sputtering and having a reduced amount ofpores, it is effective that a complex oxide containing Zn having a lowmelting point and W is present in the oxide sintered material containingIn, W and Zn at the time of sintering. To this end, it is preferable toincrease the number of contact points between the tungsten element andthe zinc element at the time of sintering so as to form a complex oxidecontaining Zn and W in the molded body in a highly dispersed state.Further, since the complex oxide containing Zn and W is formed duringthe sintering step, it is possible obtain the oxide sintered materialcapable of reducing abnormal discharge during sputtering and having areduced amount of pores at a low sintering temperature. Therefore, it ispreferable to use a preliminarily synthesized complex oxide powdercontaining Zn and

In in the manufacturing process so as to increase the number of contactpoints with W, so that an oxide sintered material capable of reducingabnormal discharge during sputtering and having a reduced amount ofpores may be obtained at a low sintering temperature.

Further, according to the method including the step of forming acalcined powder containing the Zn₄In₂O₇ crystal phase, the step ofpreparing a secondary mixture by using the calcined powder, and the stepof forming a molded body by molding the secondary mixture, the Zn₄In₂O₇crystal phase tends to remain in the oxide sintered material even afterthe sintering step, which makes it possible to obtain an oxide sinteredmaterial containing a highly dispersed Zn₄In₂O₇ crystal phase.Alternatively, the highly dispersed Zn₄In₂O₇ crystal phase may be formedby placing the molded body at the first temperature for 30 minutes orlonger. The Zn₄In₂O₇ crystal phase highly dispersed in the oxidesintered material helps to reduce abnormal discharge during sputtering,and thereby is desirable.

It is preferable that the tungsten oxide powder used for producing theoxide sintered material contains at least one crystal phase selectedfrom the group consisting of a WO₃ crystal phase, a WO₂ crystal phaseand a WO_(2.72) crystal phase, which makes it possible to obtain anoxide sintered material capable of reducing abnormal discharge duringsputtering and having a reduced amount of pores as well as asemiconductor device which includes an oxide semiconductor film formedby a sputtering method using the oxide sintered material as a sputteringtarget and capable of maintaining a high field-effect mobility even ifit is annealed at a high temperature, and thereby is advantageous. Fromthis viewpoint, the WO_(2.72) crystal phase is more preferable.

The median particle size d50 of the tungsten oxide powder is preferably0.1 μm or more and 4 μm or less, more preferably 0.2 μm or more and 2 μmor less, and further preferably 0.3 μm or more and 1.5 μm or less, whichmakes it possible to increase the apparent density and the mechanicalstrength of the oxide sintered material. The median particle size d50may be determined by BET specific surface area measurement. If themedian particle size d50 is smaller than 0.1 μm, it would be difficultto handle the powder, and it would be difficult to uniformly mix thecomplex oxide powder containing Zn and In with the tungsten oxidepowder. If the median particle size d50 is greater than 4 μm, it wouldbe difficult to reduce the amount of pores in the oxide sinteredmaterial to be obtained.

The method of manufacturing the oxide sintered material according to thepresent embodiment is not particularly limited, in order to efficientlyform the oxide sintered material of Embodiment 1, it should include thefollowing steps, for example:

(1) Step of Preparing Raw Powders

As the raw powders of the oxide sintered material, oxide powders ofmetal elements constituting the oxide sintered material such as theindium oxide powder (for example, In₂O₃ powder), the tungsten oxidepowder (for example, WO₃ powder, WO_(2.72) powder, WO₂ powder), and thezinc oxide powder (for example, ZnO powder) are prepared. If the oxidesintered material contains zirconium, then a zirconium oxide powder (forexample, ZrO₂ powder) is prepared as the raw material.

As the tungsten oxide powder, a powder having a chemical composition inwhich oxygen is deficient as compared with WO₃ powder such as WO_(2.72)powder and WO₂ powder may be used preferably, which makes it possible toobtain an oxide sintered material capable of reducing abnormal dischargeduring sputtering and having a reduced number and a semiconductor devicewhich includes an oxide semiconductor film formed by a sputtering methodusing the oxide sintered material as a sputtering target and capable ofmaintaining a high field-effect mobility even if it is annealed at ahigh temperature. From this viewpoint, it is more preferable that atleast a part of the tungsten oxide powder is the WO_(2.72) powder. Inorder to prevent the inclusion of unintentional metal elements and Siinto the oxide sintered material so as to obtain a semiconductor devicewhich includes an oxide semiconductor film formed by a sputtering methodusing an oxide sintered material as a sputtering target and has stablephysical properties, it is preferable that the purity of the raw powdersis as high as 99.9 mass % or more.

As described above, it is preferable that the median particle size d50of the tungsten oxide powder is 0.1 μm or more and 4 μm or less, whichmakes it possible to obtain an oxide sintered material havingappropriate apparent density and mechanical strength as well as reducedamount of pores.

(2) a Step of Preparing a Primary Mixture of a Zinc Oxide Powder and anIndium Ooxide Powder

Among the raw powders mentioned above, the zinc oxide powder and theindium oxide powder are mixed (or pulverized and mixed). In order toobtain a calcined powder containing a Zn₄In₂O₇ crystal phase, the In₂O₃powder serving as the indium oxide powder and the ZnO powder serving asthe zinc oxide powder are mixed so that the molar ratio ofIn₂O₃:ZnO=1:4. In order to obtain an oxide sintered material capable ofreducing abnormal discharge during sputtering and having a reducednumber and a semiconductor device which includes an oxide semiconductorfilm formed by a sputtering method using the oxide sintered material asa sputtering target and capable of maintaining a high field-effectmobility even if it is annealed at a high temperature, it is preferablethat the calcined powder contains the Zn₄In₂O₇ crystal phase.

The method of mixing the zinc oxide powder and the indium oxide powderis not particularly limited, and it may be either a dry-type method or awet-type method. Specifically, the zinc oxide powder and the indiumoxide powder may be pulverized and mixed by using a ball mill, aplanetary ball mill, a bead mill or the like. In this way, a primarymixture of the raw powders is obtained. When the mixture is obtained bythe wet-type pulverizing and mixing method, a drying method such as airdrying or spray drying may be used to dry the wet mixture.

(3) a Step of Forming a Calcined Powder From a Complex Oxide ContainingZn and In

The obtained primary mixture is heat-treated (calcined) to form acalcined powder (a complex oxide powder containing Zn and In). In orderto prevent the particle size of the calcined product from becoming toolarge so as to suppress the increase of the pores in the sinteredmaterial, the calcination temperature for the primary mixture ispreferably less than 1300° C., and in order to obtain a complex oxidepowder containing Zn and In as the calcined product and furthercontaining a Zn₄In₂O₇ crystal phase, the calcination temperature ispreferably 550° C. or more, and more preferably 1200° C. or more. Aslong as the calcination temperature is high enough to form the crystalphase, it is preferably as low as possible so as to make the particlesize of the calcined powder as small as possible. In this way, acalcined powder containing a Zn₄In₂O₇ crystal phase may be obtained. Thecalcination atmosphere may be any atmosphere as long as it containsoxygen, and preferably may be an air atmosphere having an air pressureor a pressure higher than the air pressure, or an oxygen-nitrogen mixedatmosphere containing 25 vol % or more of oxygen having an air pressureor a pressure higher than the air pressure. From the viewpoint ofimproving productivity, the air atmosphere having an air pressure or apressure around the air pressure is more preferred.

(4) a Step of Preparing a Secondary Mixture of the Raw Powders Includingthe Calcined Powder

Next, the obtained calcined powder, the indium oxide powder (forexample, In₂O₃ powder) and the tungsten oxide powder (for example,WO_(2.72) powder) are mixed (or pulverized and mixed) in the same manneras the preparation of the primary mixture. In this way, a secondarymixture of the raw powders is obtained. The zinc oxide is preferablypresent as a complex oxide with indium by the calcination step. Ifzirconium is contained in the oxide sintered material, then thezirconium oxide powder (for example, ZrO₂ powder) is mixed (orpulverized and mixed) at the same time.

The mixing method in the step is not particularly limited, and it may beeither a dry-type method or a wet-type method. Specifically, thecalcined powder, the indium oxide powder and the tungsten oxide powdermay be pulverized and mixed by using a ball mill, a planetary ball mill,a bead mill or the like. In this way, a primary mixture of the rawpowders is obtained. When the mixture is obtained by the wet-typepulverizing and mixing method, a drying methods such as air drying andspray drying may be used to dry the wet mixture.

(5) a Step of Forming a Molded Body by Molding the Secondary Mixture

Next, the obtained secondary mixture is molded. The method of moldingthe secondary mixture is not particularly limited, but from theviewpoint of improving the apparent density of the oxide sinteredmaterial, a uniaxial pressing method, a CIP (Cold Isostatic Pressing)method, a casting method or the like is preferred.

(6) a Step of Forming an Oxide Sintered Material by Sintering the MoldedBody (Sintering Step)

Next, the obtained molded body is sintered to form an oxide sinteredmaterial. At this time, if a hot press sintering method is used, itwould be difficult to obtain an oxide sintered material capable ofreducing abnormal discharge during sputtering and having a reducedamount of pores. In order to obtain an oxide sintered material capableof reducing abnormal discharge during sputtering and having a reducedamount of pores, the sintering temperature of the molded body (thesecond temperature) is preferably 800° C. or more and less than 1200°C., more preferably 900° C. or more and 1195° C. or less, and furtherpreferably 1100° C. or more and 1190° C. or less. If the secondtemperature is 800° C. or more, it is advantageous in reducing theamount of pores in the oxide sintered material, and if the secondtemperature is less than 1200° C., it is advantageous in suppressing thedeformation of the oxide sintered material so as to fit it properly tothe sputtering target. In order to obtain an oxide sintered materialcapable of reducing abnormal discharge during sputtering and having areduced amount of pores, it is preferable that the sintering atmosphereis an air atmosphere having an air pressure or a pressure around the airpressure.

As described above, in order to obtain an oxide sintered materialcapable of reducing abnormal discharge during sputtering and having areduced number of bores, before placing the molded body at the secondtemperature of 800° C. or more and less than 1200° C., it is preferableto place the molded body at a first constant temperature (lower than thesecond temperature) selected from a temperature range of 500° C. or moreand 1000° C. or less for 30 minutes or longer. This step may be aheating process in the sintering step.

Embodiment 3: Sputtering Target

The sputtering target according to the present embodiment includes theoxide sintered material of Embodiment 1. Therefore, according to thesputtering target of the present embodiment, it is possible to reduceabnormal discharge during sputtering. In addition, according to thesputtering target of the present embodiment, since the amount of poresis reduced, it is possible to provide a semiconductor device havingexcellent characteristics such as capable of maintaining a highfield-effect mobility even if it is annealed at a high temperature.

The sputtering target is used as a raw material in the sputteringmethod. The sputtering method is such a method in which a sputteringtarget and a substrate are disposed facing each other in a filmdeposition chamber, a voltage is applied to the sputtering target, whichcauses rare gas ions to sputter against the surface of the target so asto knock out atoms constituting the target from the target, and theatoms are deposited on the substrate to form a film composed of theatoms constituting the target.

In the sputtering method, the voltage applied to the sputtering targetmay be a direct current voltage. In this case, it is desired that thesputtering target is conductive. If the sputtering target has a highelectric resistance, it is impossible to apply the direct voltage, whichmakes it impossible to perform the film formation (the formation of anoxide semiconductor film) by the sputtering method. For an oxidesintered material used as a sputtering target, if a partial regionthereof has a high electric resistance and the region is wide, since nodirect current voltage is applied to the region having a high electricresistance, resulting in a problem such as that the region may not besputtered appropriately. In other words, abnormal discharge calledarcing may occur in the region with a high electric resistance,resulting in a problem such as that the film formation may not beperformed appropriately.

The pores in the oxide sintered material are vacancies, each of whichcontains gas such as nitrogen, oxygen, carbon dioxide, moisture or thelike. When such oxide sintered material is used as a sputtering target,the gas is released from the pores in the oxide sintered material,degrading the degree of vacuum of the sputtering apparatus, whichconsequently deteriorates the characteristics of the obtained oxidesemiconductor film, or alternatively causing abnormal discharge to occurfrom the edge of the pore. Therefore, it is preferred to use an oxidesintered material with a small amount of pores as the sputtering target.

In order to be suitably used in a sputtering method so as to form anoxide semiconductor film of a semiconductor device capable ofmaintaining a high field-effect mobility even when it is annealed at ahigh temperature, the sputtering target according to the presentembodiment preferably includes the oxide sintered material of Embodiment1, and more preferably it is made of the oxide sintered material ofEmbodiment 1.

Embodiment 4:Semiconductor Device and Manufacturing Method Thereof

Referring to FIGS. 1A and 1B, a semiconductor device 10 according to thepresent embodiment includes an oxide semiconductor film 14 formed by asputtering method using the sputtering target of Embodiment 3. Since thesemiconductor device according to the present embodiment includes theoxide semiconductor film 14, it may have excellent characteristics suchas capable of maintaining a high field-effect mobility even if it isannealed at a high temperature.

The semiconductor device 10 according to the present embodiment is notparticularly limited, but it is preferably a TFT (Thin Film Transistor),for example, which makes it possible to maintain the field-effectmobility high even if it is annealed at a high temperature. The oxidesemiconductor film 14 included in the TFT is preferably a channel layer,which makes it possible to maintain the field-effect mobility high evenif it is annealed at a high temperature.

The oxide semiconductor 14 may further contain zirconium (Zr), and thecontent thereof may be, for example, 1×10¹⁷ atm/cm³ or more and 1×10²⁰atm/cm³ or less. Element Zr may be contained in the oxide sinteredmaterial. The oxide semiconductor film 14 formed by using an oxidesintered material containing Zr as a raw material contains Zr. Thepresence of Zr is preferable from the viewpoint that the field-effectmobility may be kept high even if it is annealed at a high temperature.

The presence and the content of Zr may be determined by using asecondary ion mass spectrometer.

In the semiconductor device of the present embodiment, the oxidesemiconductor film 14 preferably has an electrical resistivity of 10⁻¹Ωcm or more. Although many transparent conductive films containingindium oxide have been investigated so far, in the application of atransparent conductive film, it is required that the electricalresistivity thereof is smaller than 10⁻¹ Ωcm. On the other hand, sincethe oxide semiconductor film 14 included in the semiconductor device ofthe present embodiment preferably has an electrical resistivity of 10⁻¹Ωcm or more, it may be suitably used as a channel layer of asemiconductor device. If a film has an electrical resistivity smallerthan 10⁻¹ Ωcm, it is difficult for it to be used as a channel layer of asemiconductor device.

The oxide semiconductor film 14 may be obtained by a manufacturingmethod including a step of forming a film according to the sputteringmethod. The sputtering method has been described in the above.

A magnetron sputtering method, a facing target magnetron sputteringmethod or the like may be used as the sputtering method. As theatmosphere gas for the sputtering, Ar gas, Kr gas or Xe gas may be used,and oxygen may be mixed with these gases.

Further, it is preferable that the oxide semiconductor film 14 issubjected to a heat treatment (annealing) after the film formation bythe sputtering method. The oxide semiconductor film 14 obtained by thismethod is advantageous since it is possible for a semiconductor device(for example, a TFT) including the oxide semiconductor film as a channellayer to maintain the field-effect mobility high even if it is annealedat a high temperature.

The heat treatment after the film formation by the sputtering method maybe performed by heating the semiconductor device. In order to obtainhigh characteristics when it is used as a semiconductor device, it ispreferable to perform the heat treatment. The heat treatment may beperformed immediately after forming the oxide semiconductor film 14 orafter forming a source electrode, a drain electrode, an etch stopperlayer (ES layer), a passivation film and the like. In order to obtainhigh characteristics when it is used as a semiconductor device, it ismore preferable to perform the heat treatment after forming the etchstopper layer.

If the heat treatment is performed after forming the oxide semiconductorfilm 14, the substrate temperature is preferably 100° C. or more and500° C. or less. The atmosphere for the heat treatment may be anyatmosphere such as air atmosphere, nitrogen gas, nitrogen gas-oxygengas, Ar gas, Ar-oxygen gas, water vapor-containing atmosphere, watervapor-containing nitrogen or the like. The pressure of the atmospheremay be air pressure, under a depressurized condition (for example, lessthan 0.1 Pa from normal pressure), or under a pressurized condition (forexample, 0.1 Pa to 9 MPa over normal pressure), but it is preferably airpressure. The time for the heat treatment may be, for example, about 3minutes to 2 hours, and preferably about 10 minutes to 90 minutes.

In order to obtain higher characteristics (for example, reliability)when it is used as a semiconductor device, it is desirable that the heattreatment is performed at a higher temperature. However, if thetemperature for the heat treatment is raised, the field-effect mobilityof the In—Ga—Zn—O-based oxide semiconductor film may be deteriorated.However, if a semiconductor device (for example, a TFT) includes, as achannel layer, the oxide semiconductor film 14 obtained by thesputtering method using the oxide sintered material according toEmbodiment 1 as a sputtering target, it is possible for thesemiconductor device to maintain a high field-effect mobility even if itis annealed at a high temperature, which is advantageous.

FIGS. 1A, 1B, 2 and 3 are schematic diagrams illustrating some examplesof a semiconductor device (TFT) according to the present embodiment. Thesemiconductor device 10 illustrated in FIGS. 1A and 1B includes asubstrate 11, a gate electrode 12 disposed on the substrate 11, a gateinsulating film 13 disposed as an insulating layer on the gate electrode12, a gate insulating film 13, the oxide semiconductor film 14 disposedas a channel layer on the gate insulating film 13, and a sourceelectrode 15 and a drain electrode 16 disposed on the oxidesemiconductor film 14 without contacting each other.

A semiconductor device 20 illustrated in FIG. 2 is the same as thesemiconductor device 10 illustrated in FIGS. 1A and 1B except that itfurther includes an etch stopper layer 17 which is disposed on the gateinsulating film 13 and the oxide semiconductor film 14 and is providedwith a contact hole, and a passivation film 18 which is disposed on theetch stopper layer 17, the source electrode 15 and the drain electrode16. Similar to the semiconductor device 10 illustrated in FIGS. 1A and1B, the passivation film 18 may not be disposed in the semiconductordevice 20 illustrated in FIG. 2. A semiconductor device 30 illustratedin FIG. 3 is the same as the semiconductor device 10 illustrated inFIGS. 1A and 1B except that it further includes a passivation film 18disposed on the gate insulating film 13, the source electrode 15 and thedrain electrode 16.

Next, an exemplary method of manufacturing the semiconductor deviceaccording to the present embodiment will be described. The method ofmanufacturing the semiconductor device includes a step of preparing thesputtering target of the above embodiment and a step of forming theoxide semiconductor film by a sputtering method using the sputteringtarget. First, the method of manufacturing the semiconductor device 10illustrated in FIGS. 1A and 1B will be described. Although themanufacturing method is not particularly limited, from the viewpoint ofefficiently manufacturing the semiconductor device 10 with highcharacteristics, with reference to FIGS. 4A to 4D, it is preferred thatthe manufacturing method includes a step of forming the gate electrode12 on the substrate 11 (FIG. 4A), a step of forming the gate insulatingfilm 13 as a insulating layer on the gate electrode 12 and the substrate11 (FIG. 4B), a step of forming the oxide semiconductor film 14 as achannel layer on the gate insulating film 13 (FIG. 4C), and a step offorming the source electrode 15 and the drain electrode 16 on the oxidesemiconductor film 14 without contacting each other (FIG. 4D).

(1) Step of Forming Gate Electrode

With reference to FIG. 4A, the gate electrode 12 is formed on thesubstrate 11. The substrate 11 is not particularly limited, but from theviewpoint of improving the transparency, the price stability and thesurface smoothness, it is preferably a quartz glass substrate, anon-alkali glass substrate, an alkali glass substrate or the like. Thegate electrode 12 is not particularly limited, but from the viewpoint ofhaving a high oxidation resistance and a low electric resistance, it ispreferably a Mo electrode, a Ti electrode, a W electrode, an Alelectrode, a Cu electrode or the like. The method of forming the gateelectrode 12 is not particularly limited, but from the viewpoint ofuniformly forming the gate electrode 12 with a large area on the mainsurface of the substrate 11, it is preferable to use a vacuum vapordeposition method, a sputtering method or the like. As illustrated inFIG. 4A, in the case of forming the gate electrode 12 partially on thesurface of the substrate 11, an etching method using a photoresist maybe adopted.

(2) Step of Forming Gate Insulating Film

With reference to FIG. 4B, the gate insulating film 13 is formed as aninsulating layer on the gate electrode 12 and the substrate 11. Themethod of forming the gate insulating film 13 is not particularlylimited, but from the viewpoint of uniformly forming the gate insulatingfilm 13 with a large area and ensuring the insulating property, it ispreferable to use a plasma CVD (Chemical Vapor Deposition) method or thelike.

The material for the gate insulating film 13 is not particularlylimited, but from the viewpoint of ensuring the insulating property, itis preferably silicon oxide (SiO_(x)), silicon nitride (SiN_(y)) or thelike.

(3) Step of Forming Oxide Semiconductor Film

With reference to FIG. 4C, the oxide semiconductor film 14 is formed asa channel layer on the gate insulating film 13. As described above, theoxide semiconductor film 14 is formed in a film formation process by thesputtering method. As the raw material target (sputtering target) forthe sputtering method, the oxide sintered material of Embodiment 1 isused.

In order to obtain high characteristics (for example, reliability) whenit is used as a semiconductor device, it is preferable to perform a heattreatment (annealing) after the film formation by the sputtering method.The heat treatment may be performed immediately after the formation ofthe oxide semiconductor film 14 or after forming the source electrode15, the drain electrode 16, the etch stopper layer 17, the passivationfilm 18 or the like. In order to obtain high characteristics (forexample, reliability) when it is used as a semiconductor device, it ismore preferable to perform the heat treatment after forming the etchstopper layer 17. If the heat treatment is performed after forming theetch stopper layer 17, the heat treatment may be performed before orafter the formation of the source electrode 15 and the drain electrode16, but preferably before the formation of the passivation film 18.

(4) Step of Forming Source Electrode and Drain Electrode

With reference to FIG. 4D, the source electrode 15 and the drainelectrode 16 are formed on the oxide semiconductor film 14 withoutcontacting each other. Each of the source electrode 15 and the drainelectrode 16 is not particularly limited, but from the viewpoint ofhaving a high oxidation resistance, a low electric resistance and a lowcontact electric resistance with the oxide semiconductor film 14, it ispreferably a Mo electrode, a Ti electrode, a W electrode, an Alelectrode, a Cu electrode or the like. The method of forming the sourceelectrode 15 and the drain electrode 16 is not particularly limited, butfrom the viewpoint of uniformly forming the source electrode 15 and thedrain electrode 16 with a large area on the oxide semiconductor film 14formed on the main surface of the substrate 11, it is preferable to usea vacuum vapor deposition method, a sputtering method or the like. Themethod of forming the source electrode 15 and the drain electrode 16without contacting each other is not particularly limited, but from theviewpoint of forming a uniform pattern of the source electrode 15 andthe drain electrode 16 with a large area, an etching method using aphotoresist is preferable.

Next, a method of manufacturing the semiconductor device 20 illustratedin FIG. 2 will be described. The method of manufacturing thesemiconductor device 20 is the same as the method of manufacturing thesemiconductor device 10 illustrated in FIGS. 1A and 1B except that itfurther includes a step of forming the etch stopper layer 17 providedwith a contact hole 17 a and a step of forming the passivation film 18.Specifically, with reference to FIGS. 4A to 4D and FIGS. 5A to 5D, it ispreferable that the method of manufacturing the semiconductor device 20includes a step of the gate electrode 12 on the substrate 11 (FIG. 4A),a step of forming the gate insulating film 13 as an insulating layer onthe gate electrode 12 and the substrate 11 (FIG. 4B), a step of formingthe oxide semiconductor film 14 as a channel layer on the gateinsulating film 13 (FIG. 4C), a step of forming the etch stopper layer17 on the oxide semiconductor film 14 and the gate insulating film 13(FIG. 5A), a step of forming the contact hole 17 a in the etchingstopper layer 17 (FIG. 5B), a step of forming the source electrode 15and the drain electrode 16 on the oxide semiconductor film 14 and theetch stopper layer 17 without contacting each other (FIG. 5C), and astep of forming the passivation film 18 on the etch stopper layer 17,the source electrode 15 and the drain electrode 16 (FIG. 5D).

The material for the etch stopper layer 17 is not particularly limited,but from the viewpoint of ensuring the insulating property, it ispreferably silicon oxide (SiO_(x)), silicon nitride (SiN_(y)), aluminumoxide (Al_(m)O_(n)) or the like. The etch stopper layer 17 may be acombination of films made of different materials. The method of formingthe etch stopper layer 17 is not particularly limited, but from theviewpoint of uniformly forming the etch stopper layer 17 with a largearea and ensuring the insulation property, it is preferable to use aplasma CVD (Chemical Vapor Deposition) method, a sputtering method, avacuum vapor deposition method or the like.

Since it is necessary to bring the source electrode 15 and the drainelectrode 16 into contact with the oxide semiconductor film 14, afterforming the etch stopper layer 17 on the oxide semiconductor film 14,the contact hole 17 a is formed in the etch stopper layer 17 (FIG. 5B).As a method of forming the contact hole 17 a, a dry etching method or awet etching method may be given. By etching the etch stopper layer 17according to the dry etching method or the wet etching method so as toform the contact hole 17 a, the surface of the oxide semiconductor film14 is exposed at the etched portion.

In the method of manufacturing the semiconductor device 20 illustratedin FIG. 2, similar to the manufacturing method of the semiconductordevice 10 illustrated in FIGS. 1A and 1B, after the source electrode 15and the electrodes 16 are formed on the oxide semiconductor film 14 andthe etch stopper layer 17 without contacting each other (FIG. 5C), thepassivation film 18 is formed on the etch stopper layer 17, the sourceelectrode 15 and the drain electrode 16 (FIG. 5D).

The material for the passivation film 18 is not particularly limited,but from the viewpoint of ensuring the insulating property, it ispreferably silicon oxide (SiO_(x)), silicon nitride (SiN_(y)), aluminumoxide (Al_(m)O_(n)) or the like. The passivation film 18 may be acombination of films made of different materials. The method of formingthe passivation film 18 is not particularly limited, but from theviewpoint of uniformly forming the passivation film 18 with a large areaand ensuring the insulation property, it is preferable to use a plasmaCVD (Chemical Vapor Deposition) method, a sputtering method, a vacuumvapor deposition method or the like.

Further, as the semiconductor device 30 illustrated in FIG. 3, it isacceptable that a back channel etch (BCE) structure is adopted, andinstead of forming the etch stopper layer 17, the passivation film 18 isdirectly formed on the gate insulating film 13, the oxide semiconductorfilm 14, the source electrode 15 and the drain electrode 16. In thiscase, the passivation film 18 may be the same as the passivation film 18of the semiconductor device 20 illustrated in FIG. 2.

(5) Other Steps

Finally, the heat treatment (annealing) is performed. The heat treatmentmay be carried out by heating the semiconductor device formed on thesubstrate.

The temperature for heating the semiconductor device in the heattreatment is preferably 100° C. or more and 500° C. or less, and morepreferably 400° C. or more. The atmosphere for the heat treatment may beany atmosphere such as air atmosphere, nitrogen gas, nitrogen gas-oxygengas, Ar gas, Ar-oxygen gas, water vapor-containing atmosphere, watervapor-containing nitrogen or the like. Preferably, it is an inertatmosphere such as nitrogen or Ar gas. The pressure of the atmospheremay be air pressure, under a depressurized condition (for example, lessthan 0.1 Pa), or under a pressurized condition (for example, 0.1 Pa to 9MPa), but it is preferably air pressure. The time for the heat treatmentmay be, for example, about 3 minutes to 2 hours, and preferably about 10minutes to 90 minutes.

In order to obtain higher characteristics (for example, reliability)when it is used as a semiconductor device, it is desirable that the heattreatment is performed at a higher temperature. However, if thetemperature for the heat treatment is raised, the field-effect mobilityof the In—Ga—Zn—O-based oxide semiconductor film may be deteriorated.However, if a semiconductor device (for example, a TFT) includes, as achannel layer, the oxide semiconductor film 14 obtained by thesputtering method using the oxide sintered material according toEmbodiment 1 as a sputtering target, it is possible for thesemiconductor device to maintain a high field-effect mobility even if itis annealed at a high temperature, which is advantageous.

EXAMPLES Examples 1 to 22

(1) Production of Oxide Sintered Material

(1-1) Preparation of Raw Powders

The following powders were prepared: a tungsten oxide powder (denoted as“W” in Table 1) having a composition (listed in the column of “W powder”in Table 1), a median particle size d50 (denoted as in the column of “WParticle Size” in Table 1) and a purity of 99.99 mass %; a ZnO powder(denoted as “Z” in Table 1) having a median particle size d50 of 1.0 μmand a purity of 99.99 mass %; an In₂O₃ powder (denoted as “I” inTable 1) having a median particle size d50 of 1.0 μm and a purity of99.99 mass %; and a ZrO₂ powder (denoted as “R” in Table 1) having amedian particle size d50 of 1.0 μm and a purity of 99.99 mass %.

(1-2) Preparation of Raw Powder Mixture

The prepared raw powders, i.e., the In₂O₃ powder, the ZnO powder, thetungsten oxide powder and the ZrO₂ powder were firstly charged into apot and then introduced into a ball mill, pulverized and mixed for 12hours to prepare a raw powder mixture. The mixing ratio of the rawpowders was set such that the molar ratio of In, Zn, W and Zr in themixture was as shown in Table 1. During the pulverization and mixing,pure water was used as a dispersion medium. The obtained raw powdermixture was dried by spray drying.

(1-3) Formation of Molded Body by Molding Mixture

Next, the obtained raw powder mixture was molded by pressing, and thenpress-molded according to the CIP method in static water at roomtemperature (5° C. to 30° C.) under a pressure of 190 MPa to obtain adisk-shaped molded body having a diameter of 100 mm and a thickness ofabout 9 mm.

(1-4) Formation of Oxide Sintered Material by Sintering Molded Body(Sintering Step)

Next, the obtained molded body was sintered for 8 hours at a sinteringtemperature (the second temperature) shown in Table 1 in an airatmosphere under atmospheric pressure to obtain an oxide sinteredmaterial containing an In₂O₃ crystal phase, a Zn₄In₂O₇ crystal phase anda ZnWO₄ crystal phase. The retention temperature (the first temperature)and the retention time in the heating process of the sintering step areshown in Table 1.

(2) Evaluation of Physical Properties of Oxide Sintered Material

(2-1) Identification of In₂O₃ Crystal Phase, Zn₄In₂O₇ Crystal Phase andZnWO₄ Crystal Phase

A sample was taken from a portion having a depth of 2 mm or more fromthe outermost surface of the obtained oxide sintered material andsubjected to crystal analysis by X-ray diffraction method. Themeasurement conditions for X-ray diffraction were as follows.

(Measurement Conditions of X-Ray Diffraction)

θ-2θ method,

X-ray source: Cu Kα ray,

X-ray tube voltage: 45 kV,

X-ray tube current: 40 mA,

Step width: 0.02°,

Step time: 1 second/step,

Measurement range 20:10° to 80°.

According to the identification of the diffraction peaks, it wasconfirmed that the oxide sintered material of each of Examples 1 to 22contains all of the In₂O₃ crystal phase, the Zn₄In₂O₇ crystal phase andthe ZnWO₄ crystal phase.

(2-2) X-ray Diffraction Peak Derived from In₂O₃ Crystal Phase

According to the X-ray diffraction measurement described in the above(2-1), the diffraction angle 2θ at the X-ray diffraction peak derivedfrom the In₂O₃ crystal phase was determined. The results are shown inthe column of “I angle” in Table 2. The diffraction angle 2θ at theX-ray diffraction peak derived from the In₂O₃ crystal phase in the oxidesintered material of each of Examples 1 to 22 was greater than 50.70°and smaller than 51.04°.

(2-3) Lattice Constant of C-plane of Zn₄In₂O₇ Crystal Phase

According to the X-ray diffraction measurement described in the above(2-1), the lattice constant of the C-plane of the Zn₄In₂O₇ crystal phasewas determined. The diffraction peak from the C-plane of the Zn₄In₂O₇crystal phase may appear in the range of 20=31.5° or more and less than32.8°. The lattice constant of the C-plane was calculated from thediffraction angle 2θ at the maximum peak position according to theequation of 2dsinθ=λ (Bragg's equation), wherein λ is the wavelength ofthe X-ray. The results are shown in the column of “C-plane” in Table 2.The lattice constant of the C-plane of the Zn₄In₂O₇ crystal phase in theoxide sintered material of each of Examples 1 to 22 was 33.53 Å or moreand 34.00 Å or less.

(2-4) Content of Each Crystal Phase

According to the RIR method based on the X-ray diffraction measurementdescribed in the above (2-1), the content (mass %) of each of the In₂O₃crystal phase (I crystal phase), the Zn₄In₂O₇ crystal phase (IZ crystalphase) and the ZnWO₄ crystal phase (ZW crystal phase) was quantified.The results are shown as in “I”, “IZ” and “ZW” under the column of“content of crystal phase” in Table 2, respectively.

(2-5) Element Content in Oxide Sintered Material

The contents of In, Zn, W and Zr in the oxide sintered material weremeasured by ICP emission spectrometry. Further, the Zn/W ratio (theratio of the Zn content relative to the W content) was calculated fromthe obtained Zn content and W content. The results are shown in “In”,“Zn”, “W”, “Zr”, “Zn/W ratio” under the column of “element content” inTable 2, respectively. The unit of the In content, the Zn content andthe W content is atom %, the unit of the Zr content is ppm based on thenumber of atoms, and the Zn/W ratio is the ratio of atom numbers.

(2-6) Amount of Pores in Oxide Sintered Material

A sample was taken from a portion having a depth of 2 mm or more fromthe outermost surface of the oxide sintered material immediately aftersintering. The obtained sample was ground by using a surface grindingmachine, the surface of the sample was polished by using a lappingmachine, and finally polished by using a cross section polisher, andthen subjected to SEM observation. The pores appears black in abackscattered electron image observed under a field of view of 500times. The image was binarized, and the ratio of the area of the blackportions relative to the whole area of the image was calculated. Threefields of view were selected such that the regions did not overlap, andthe average value of the area ratios for these regions was calculated asthe amount of pores (area %). The results are shown in the column of“amount of pores” in Table 2.

(3) Production of Sputtering Target

The obtained oxide sintered material was processed to have a size of 3inches (76.2 mm) in diameter×6 mm in thickness, and then attached to acopper backing plate using indium metal.

(4) Production and Evaluation of Semiconductor Device (TFT) IncludingOxide Semiconductor Film

(4-1) Measurement of Arcing Frequency During Sputtering

The produced sputtering target was placed in a film deposition chamberof a sputtering apparatus. The sputtering target was water cooledthrough the intermediary of the copper backing plate. The filmdeposition chamber was depressurized to have a degree of vacuum of about6×10⁻⁵ Pa, and the target was sputtered as follows.

Ar (argon) gas only was introduced into the film formation chamber untilthe inner pressure reached 0.5 Pa. DC power of 450 W was applied to thetarget so as to induce a sputtering discharge and held for 60 minutes.The sputtering discharge was continuously induced for 30 minutes. Thearcing frequency for each of Examples and Comparative Examples shown inTable 2 was measured by using an arc counter (arcing frequency countingdevice) attached to the DC power supply. The results are shown in thecolumn of “arcing frequency” in Table 3.

(4-2) Production of Semiconductor Device (TFT) Including OxideSemiconductor Film

A TFT having a similar structure to the semiconductor device 30illustrated in

FIG. 3 was produced by the following procedure. With reference to FIG.4A, first, a synthetic quartz glass substrate having a dimension of 50mm×50 mm×0.6 mm in thickness was prepared as the substrate 11, and a Moelectrode having a thickness of 100 nm was formed on the substrate 11according to a sputtering method as the gate electrode 12. Next, asillustrated in FIG. 4A, the gate electrode 12 was processed into apredetermined shape through etching by using a photoresist.

Next, with reference to FIG. 4B, a SiO_(x) film having a thickness of200 nm was formed on the gate electrode 12 and the substrate 11according to a plasma CVD method as the gate insulating film 13.

Next, with reference to FIG. 4C, the oxide semiconductor film 14 with athickness of 30 nm was formed on the gate insulating film 13 accordingto the DC (direct current) magnetron sputtering method. A flat surfaceof the target with a diameter of 3 inches (76.2 mm) was used as thesputtering surface. The oxide sintered material obtained in the above(1) was used as the target.

The formation of the oxide semiconductor film 14 will be described inmore detail. On a substrate holder which is water-cooled in the filmdeposition chamber of a sputtering apparatus (not shown), the substrate11, on which the gate electrode 12 and the gate insulating film 13 areformed, was arranged in such a manner that the gate insulating film 13was exposed. The target was disposed to face the gate insulating film 13with a distance of 90 mm. The film deposition chamber was depressurizedto have a degree of vacuum of about 6×10⁻⁵ Pa, and the target wassputtered as follows.

First, in a state in which a shutter was inserted between the gateinsulating film 13 and the target, a gas mixture of Ar (argon) gas andO₂ (oxygen) gas was introduced into the film formation chamber until theinner pressure reached 0.5 Pa. The content of O₂ gas in the gas mixturewas 20% by volume. DC power 450 W was applied to the sputtering targetto induce sputtering discharge so as to clean (pre-sputter) the surfaceof the target for 5 minutes.

Next, while the DC power of the same value as described in the above wasbeing applied to the same target as described in the above and theatmosphere in the film formation chamber was maintained to be unchanged,the shutter was removed so as to form the oxide semiconductor film 14 onthe gate insulating film 13. It should be noted that no bias voltage wasparticularly applied to the substrate holder. Moreover, the substrateholder was water cooled.

As described above, the oxide semiconductor film 14 was formed by the DC(direct current) magnetron sputtering method using the targetmanufactured from the oxide sintered material obtained in the above (1).The oxide semiconductor film 14 serves as a channel layer in the TFT.The film thickness of the oxide semiconductor film 14 was 30 nm (thesame applies to the other examples and comparative examples).

Next, the obtained oxide semiconductor film 14 was partially etched toform a source electrode formation portion 14 s, a drain electrodeformation portion 14 d, and a channel portion 14 c. The size of the mainsurface of each of the source electrode formation portion 14 s and thedrain electrode formation portion 14 d was set to 50 μm×50 μm, a channellength C_(L) (with reference to FIG. 1A and FIG. 1B, the channel lengthC_(L) refers to a distance of the channel portion 14 c between thesource electrode 15 and the drain electrode 16) was set to 30 μm, and achannel width C_(W) (with reference to FIG. 1A and FIG. 1B, the channelwidth C_(W) refers to the width of the channel portion 14 c) was set to40 μm. A number of 25 (at the longitudinal side)×25 (at the lateralside) of the channel portions 14 c were disposed on the substrate mainsurface of 75 mm×75 mm at a spacing of 3 mm such that a number of 25 (atthe longitudinal side)×25 (at the lateral side) of TFTs were disposed onthe substrate main surface of 75 mm×75 mm at a spacing of 3 mm.

The oxide semiconductor film 14 was partially etched in the followingmanner: an etching aqueous solution was prepared to have a volume ratioof oxalic acid:water=5:95, the substrate 11 having the gate electrode12, the gate insulating film 13 and the oxide semiconductor film 14formed thereon in this order was immersed in the etching aqueoussolution at 40° C.

With reference to FIG. 4D, the source electrode 15 and the drainelectrode 16 were then formed on the oxide semiconductor film 14,separating from each other.

Specifically, first, a resist (not shown) was applied onto the oxidesemiconductor film 14, exposed to light and developed so as to exposeonly the main surface of the oxide semiconductor film 14 correspondingto the source electrode formation portion 14 s and the drain electrodeformation portion 14 d. Next, the sputtering method was employed to formMo electrodes each having a thickness of 100 nm and serving as thesource electrode 15 and the drain electrode 16 respectively on the mainsurface of the oxide semiconductor film 14 corresponding to the sourceelectrode formation portion 14 s and the drain electrode formationportion 14 d. Then, the resist developed on the oxide semiconductor film14 was removed. One Mo electrode serving as the source electrode 15 andone Mo electrode serving as the drain electrode 16 were formed for onechannel portion 14 c such that a number of 25 (at the longitudinalside)×25 (at the lateral side) of TFTs were disposed on the substratemain surface of 75 mm×75 mm at a spacing of 3 mm.

Next, with reference to FIG. 3, the passivation film 18 was formed onthe gate insulating film 13, the oxide semiconductor film 14, the sourceelectrode 15, and the drain electrode 16. The passivation film 18 wasformed by forming a SiO_(x) film with a thickness of 200 nm by theplasma CVD method and then a SiN_(y) film with a thickness of 200 nm wasformed thereon by the plasma CVD method. In order to improvereliability, it is desirable that the oxygen content should meet thecondition that the atomic composition ratio of the SiO_(x) film iscloser to Si:O=1:2.

Next, the passivation film 18 on the source electrode 15 and the drainelectrode 16 was etched by reactive ion etching to form a contact hole,thereby partially exposing the surface of the source electrode 15 andthe surface of the drain electrode 16.

Finally, the heat treatment (annealing) was performed in nitrogenatmosphere under the atmospheric pressure. The heat treatment wasperformed for all Examples and Comparative Examples. Specifically, theheat treatment (annealing) was performed in nitrogen atmosphere at 350°C. for 60 minutes or in nitrogen atmosphere at 450° C. for 60 minutes.Thus, a TFT including the oxide semiconductor film 14 as a channel layerwas obtained.

(4-3) Evaluation on Characteristics of Semiconductor Device

The characteristics of the TFT serving as the semiconductor device 10were evaluated as follows. First, a measurement needle was brought intocontact with the gate electrode 12, the source electrode 15 and thedrain electrode 16, respectively. While a source-drain voltage V_(ds) of0.2 V was being applied between the source electrode 15 and the drainelectrode 16, a source-gate voltage V_(gs) applied between the sourceelectrode 15 and the gate electrode 12 was varied from −10 V to 15 V tomeasure a source-drain current I_(ds). Thereby, a graph was created withthe horizontal axis representing the source-gate voltage V_(gs) and thevertical axis representing the source-drain current I_(ds).

Moreover, g_(m) was derived by differentiating the source-drain currentI_(ds) with respect to the source-gate voltage V_(gs) in accordance withthe following formula [a]:g _(m) =dI _(ds) /dV _(gs)  [a]Then, the value of g_(m) when V_(gs)=10.0 V was used to determine thefield effect mobility μ_(fe) based on the following formula [b]:μ_(fe) =g _(m) ·C _(L)/(C _(W) ·C _(i) ·V _(ds))  [b]In the above formula [b], the channel length C_(L) was 30 μm and thechannel width C_(W) was 40 μm. Moreover, the capacitance C_(i) of thegate insulating film 13 was set to 3.4×10⁻⁸ F/cm², and the source-drainvoltage V_(ds) was set to 0.2 V.

The field-effect mobility μ_(fe) after the heat treatment (annealing) at350° C. for 60 minutes in the nitrogen atmosphere under the atmosphericpressure is shown in the column of “mobility (350° C.)” in Table 3, andthe field-effect mobility μ_(fe) after the heat treatment (annealing) at450° C. for 10 minutes in the nitrogen atmosphere under the atmosphericpressure is shown in the column of “mobility (450° C.)” in Table 3.Further, the ratio of the field-effect mobility after the heat treatmentat 450° C. relative to the field-effect mobility after the heattreatment at 350° C. (ratio of mobility (450° C.)/mobility (350° C.)) isshown in the column of “mobility ratio” in Table 3.

Examples 23 to 25

(1) Production of Oxide Sintered Material

(1-1) Preparation of Raw Powders

The following powders were prepared: a tungsten oxide powder (denoted as“W” in Table 1) having a composition (listed in the column of “W powder”in Table 1), a median particle size d50 (denoted as in the column of “WParticle Size” in Table 1) and a purity of 99.99 mass %; a ZnO powder(denoted as “Z” in Table 1) having a median particle size d50 of 1.0 μmand a purity of 99.99 mass %; an In₂O₃ powder (denoted as “I” inTable 1) having a median particle size d50 of 1.0 μm and a purity of99.99 mass %; and a ZrO₂ powder (denoted as “R” in Table 1) having amedian particle size d50 of 1.0 μm and a purity of 99.99 mass %.

(1-2) Preparation of Primary Mixture of Raw Powders

First, the In₂O₃ powder and the ZnO powder among the prepared rawpowders were introduced into a ball mill and were pulverized and mixedfor 18 hours to prepare a primary mixture of the raw powders. The In₂O₃powder and the ZnO powder were mixed such that the molar mixing ratio ofthe In₂O₃ powder:the ZnO powder=1:4 approximately. During thepulverization and mixing, ethanol was used as a dispersion medium. Theobtained primary mixture of the raw powders was dried in air.

(1-3) Formation of Calcined Powder by Heating Primary Mixture

Next, the obtained primary mixture of the raw powders was charged intoan alumina crucible and calcined in the air atmosphere for 8 hours at acalcination temperature shown in Table 1 to obtain a calcined powdercomposed of the Zn₄In₂O₇ crystal phase. The Zn₄In₂O₇ crystal phase wasidentified by X-ray diffraction measurement.

(1-4) Preparation of Secondary Mixture of Raw Powders Including CalcinedPowder

Next, the obtained calcined powder was charged into a pot together withthe remainder of the prepared raw powders, i.e., the In₂O₃ powder, thetungsten oxide powder and the ZrO₂ powder, which were then introducedinto a pulverization mixing ball mill and were pulverized and mixed for12 hours to prepare a secondary mixture of the raw powders. The mixingratio of the raw powders was set such that the molar ratio of In, Zn, Wand Zr in the mixture was as shown in Table 1. During the pulverizationand mixing, pure water was used as a dispersion medium. The obtainedmixed powder was dried by spray drying.

(1-5) Formation of Oxide Sintered Material

The oxide sintered material was prepared in the same manner as thatdescribed in the above (1-3) and (1-4) in <Examples 1 to 22> except thatthe secondary mixture obtained from the above (1-4) was used.

(2) Evaluation of Physical Properties of Oxide Sintered Material,Preparation of Sputtering Target, Production and Evaluation ofSemiconductor Device (TFT) Including Oxide Semiconductor Film

The evaluation of physical properties of the oxide sintered material,the preparation of a sputtering target, the production and evaluation ofa semiconductor device (TFT) including an oxide semiconductor film werecarried out in the same manner as that described in <Examples 1 to 22>.The results are shown in Table 2 and Table 3.

Comparative Example 1

(1-1) Preparation of Raw Powders

The following powders were prepared: a tungsten oxide powder (denoted as“W” in Table 1) having a composition (listed in the column of “W powder”in Table 1), a median particle size d50 (denoted as in the column of “WParticle Size” in Table 1) and a purity of 99.99 mass %; a ZnO powder(denoted as “Z” in Table 1) having a median particle size d50 of 1.0 μmand a purity of 99.99 mass %; an In₂O₃ powder (denoted as “I” inTable 1) having a median particle size d50 of 1.0 μm and a purity of99.99 mass %; and a ZrO₂ powder (denoted as “R” in Table 1) having amedian particle size d50 of 1.0 μm and a purity of 99.99 mass %.

(1-2) Preparation of Primary Mixture of Raw powders

First, the ZnO powder and the WO₃ powder among the prepared raw powderswere introduced into a ball mill and were pulverized and mixed for 18hours to prepare a primary mixture of the raw powders. The ZnO powderand the WO₃ powder were mixed such that the molar mixing ratio of theZnO powder:the WO₃ powder=1:1 approximately. During the pulverizationand mixing, ethanol was used as a dispersion medium. The obtainedprimary mixture of the raw powders was dried in air.

(1-3) Formation of Calcined Powder by Heating Primary Mixture

Next, the obtained primary mixture of the raw powders was charged intoan alumina crucible and calcined in the air atmosphere for 8 hours at acalcination temperature shown in Table 1 to obtain a calcined powdercomposed of the ZnWO₄ crystal phase. The ZnWO₄ crystal phase wasidentified by X-ray diffraction measurement.

(1-4) Preparation of Secondary Mixture of Raw powders including CalcinedPowder

Next, the obtained calcined powder was charged into a pot together withthe remainder of the prepared raw powders, i.e., the In₂O₃ powder, theZnO powder and the ZrO₂ powder, which were then introduced into apulverization mixing ball mill and were pulverized and mixed for 12hours to prepare a secondary mixture of the raw powders. The mixingratio of the raw powders was set such that the molar ratio of In, Zn, Wand Zr in the mixture was as shown in Table 1. During the pulverizationand mixing, pure water was used as a dispersion medium. The obtainedmixed powder was dried by spray drying.

(1-5) Formation of Oxide Sintered Material

The oxide sintered material was prepared in the same manner as thatdescribed in the above (1-3) and (1-4) in <Examples 1 to 22> except thatthe secondary mixture obtained from the above (1-4) was used and that noheating process is included in the sintering step.

(2) Evaluation of Physical Properties of Oxide Sintered Material,Preparation of Sputtering Target, Production and Evaluation ofSemiconductor Device (TFT) Including Oxide Semiconductor Film

The evaluation of physical properties of the oxide sintered material,the preparation of a sputtering target, the production and evaluation ofa semiconductor device (TFT) including an oxide semiconductor film werecarried out in the same manner as that described in <Examples 1 to 22>.The results are shown in Table 2 and Table 3. The presence of theZn₄In₂O₇ crystal phase was not confirmed in the oxide sintered materialof Comparative Example 1.

Comparative Example 2

(1-1) Preparation of Raw Powders

The following powders were prepared: a tungsten oxide powder (denoted as“W” in Table 1) having a composition (listed in the column of “W powder”in Table 1), a median particle size d50 (denoted as in the column of “WParticle Size” in Table 1) and a purity of 99.99 mass %; a ZnO powder(denoted as “Z” in Table 1) having a median particle size d50 of 1.0 μmand a purity of 99.99 mass %; an In₂O₃ powder (denoted as “I” inTable 1) having a median particle size d50 of 1.0 μm and a purity of99.99 mass %; and a ZrO₂ powder (denoted as “R” in Table 1) having amedian particle size d50 of 1.0 μm and a purity of 99.99 mass %.

(1-2) Preparation of Primary Mixture of Raw Powder

First, the In₂O₃ powder and the WO₃ powder among the prepared rawpowders were introduced into a ball mill and were pulverized and mixedfor 18 hours to prepare a primary mixture of the raw powders. The molarmixing ratio of the In₂O₃ powder and the WO₃ powder were mixed such thatthe molar mixing ratio of the In₂O₃ powder:the WO₃ powder=1:12approximately. During the pulverization and mixing, ethanol was used asa dispersion medium. The obtained primary mixture of the raw powders wasdried in air.

(1-3) Formation of Calcined Powder by Heating of Primary Mixture

Next, the obtained primary mixture of the raw powders was charged intoan alumina crucible and calcined in the air atmosphere for 8 hours at acalcination temperature shown in Table 1 to obtain a calcined powdercomposed of the In W₆O₁₂crystal phase. The InW₆O₁₂crystal phase wasidentified by X-ray diffraction measurement.

(1-4) Preparation of Secondary Mixture of Raw Powder Containing CalcinedPowder

Next, the obtained calcined powder was charged into a pot together withthe remainder of the prepared raw powders, i.e., the In₂O₃ powder, theZnO powder and the ZrO₂ powder, which were then introduced into apulverization mixing ball mill and were pulverized and mixed for 12hours to prepare a secondary mixture of the raw powders. The mixingratio of the raw powders was set such that the molar ratio of In, Zn, Wand Zr in the mixture was as shown in Table 1. During the pulverizationand mixing, pure water was used as a dispersion medium. The obtainedmixed powder was dried by spray drying.

(1-5) Formation of Oxide Sintered Material

The oxide sintered material was prepared in the same manner as thatdescribed in the above (1-3) and (1-4) in <Examples 1 to 22> except thatthe secondary mixture obtained from the above (1-4) was used and that noheating process is included in the sintering step.

(2) Evaluation of Physical Properties of Oxide Sintered Material,Preparation of Sputtering Target, Production and Evaluation ofSemiconductor Device (TFT) Including Oxide Semiconductor Film

The evaluation of physical properties of the oxide sintered material,the preparation of a sputtering target, the production and evaluation ofa semiconductor device (TFT) including an oxide semiconductor film werecarried out in the same manner as that described in <Examples 1 to 22>.The results are shown in Table 2 and Table 3. The presence of theZn₄In₂O₇ crystal phase was not confirmed in the oxide sintered materialof Comparative Example 2.

Comparative Example 3

(1) Production of Oxide Sintered Material

(1-1) Preparation of Raw Powders

The following powders were prepared: a tungsten oxide powder (denoted as“W” in Table 1) having a composition (listed in the column of “W powder”in Table 1), a median particle size d50 (denoted as in the column of “WParticle Size” in Table 1) and a purity of 99.99 mass %; a ZnO powder(denoted as “Z” in Table 1) having a median particle size d50 of 1.0 μmand a purity of 99.99 mass %; an In₂O₃ powder (denoted as “I” inTable 1) having a median particle size d50 of 1.0 μm and a purity of99.99 mass %; and a ZrO₂ powder (denoted as “R” in Table 1) having amedian particle size d50 of 1.0 μm and a purity of 99.99 mass %.

(1-2) Preparation of Mixture of Raw Powders

The prepared raw powders were charged into a pot, then introduced into aball mill and were pulverized and mixed for 12 hours to prepare amixture of the raw powders. The mixing ratio of the raw powders was setsuch that the molar ratio of In, Zn, W and Zr in the mixture was asshown in Table 1. During the pulverization and mixing, pure water wasused as a dispersion medium. The obtained mixed powder was dried byspray drying.

(1-3) Formation of Oxide Sintered Material

The oxide sintered material was prepared in the same manner as thatdescribed in the above (1-3) and (1-4) in <Examples 1 to 22> except thatthe secondary mixture obtained from the above (1-4) was used and that noheating process is included in the sintering step.

(2) Evaluation of Physical Properties of Oxide Sintered Material,Preparation of Sputtering Target, Production and Evaluation ofSemiconductor Device (TFT) Including Oxide Semiconductor Film

The evaluation of physical properties of the oxide sintered material,the preparation of a sputtering target, the production and evaluation ofa semiconductor device (TFT) including an oxide semiconductor film werecarried out in the same manner as that described in <Examples 1 to 22>.The results are shown in Table 2 and Table 3. The presence of theZn₄In₂O₇ crystal phase was not confirmed in the oxide sintered materialof Comparative Example 3.

TABLE 1 Molar Mixing Ratio I Z W R W Particle Calcination RetentionTemperature Retention Sintering Temperature (mole (mole (mole (mole WSize Temperature (First Temperature) Time (Second Temperature) %) %) %)%) Powder (μm) (° C.) (° C.) (min) (° C.) Example 1 94.7 3.9 1.4 0.049WO_(2.72) 1.2 — 600 60 1185 Example 2 68.5 30.3 1.2 0.025 WO_(2.72) 1.1— 600 60 1185 Example 3 65.7 33.1 1.2 0.025 WO_(2.72) 1.1 — 600 60 1185Example 4 50.7 48.2 1.1 0.023 WO_(2.72) 1 — 600 60 1185 Example 5 93.83.9 2.3 0.048 WO_(2.72) 1.2 — 600 60 1185 Example 6 67.8 30.2 2.0 0.025WO_(2.72) 1.1 — 600 60 1185 Example 7 65.0 33.0 2.0 0.041 WO_(2.72) 1.1— 600 60 1185 Example 8 50.1 48.0 1.8 0.023 WO_(2.72) 1 — 600 60 1185Example 9 92.3 3.8 3.8 0.048 WO_(2.72) 1.5 — 600 60 1185 Example 10 92.13.8 3.8 0.211 WO₃ 0.8 — 600 60 1185 Example 11 78.5 17.8 3.6 0.045WO_(2.72) 0.9 — 600 60 1185 Example 12 66.6 30.0 3.3 0.075 WO_(2.72) 1 —600 60 1185 Example 13 66.6 30.0 3.3 0.042 WO_(2.72) 0.9 — 600 60 1185Example 14 63.9 32.8 3.3 0.041 WO_(2.72) 1.2 — 600 60 1185 Example 1549.2 47.7 3.0 0.037 WO_(2.72) 1.3 — 600 60 1185 Example 16 49.3 47.8 3.00.003 WO₃ 0.7 — 600 60 1185 Example 17 65.3 29.7 5.0 0.041 WO_(2.72) 1.5— 600 60 1185 Example 18 62.6 32.5 4.9 0.041 WO_(2.72) 1.6 — 600 60 1185Example 19 48.1 47.4 4.4 0.037 WO₃ 1.4 — 600 60 1185 Example 20 58.728.6 12.7 0.040 WO₃ 1.8 — 600 60 1185 Example 21 56.2 31.2 12.5 0.039WO₃ 1.4 — 600 60 1185 Example 22 42.8 45.7 11.4 0.036 WO₃ 1.6 — 600 601185 Example 23 56.2 28.1 15.6 0.039 WO₃ 2 1200 600 60 1185 Example 2453.8 30.8 15.4 0.038 WO₃ 1.5 1200 600 60 1185 Example 25 40.8 45.1 14.10.035 WO₃ 1.5 1200 600 60 1185 Comparative Example 1 65.0 33.0 2.0 0.041WO₃ 3.5  550 — — 1185 Comparative Example 2 65.0 33.0 2.0 0.041 WO₃ 3.51000 — — 1185 Comparative Example 3 65.0 33.0 2.0 0.041 WO₃ 3.5 — — —1185

TABLE 2 Element Content Content of Crystal Phase Amount of In Zn W Zr IIZ ZW I Angle C-Plane Bores (atom %) (atom %) (atom %) (ppm) Zn/W 

(mass %) (mass %) (mass %) (°) (Å) (area %) Example 1 97.3 2 0.7 15 2.998.2 0.9 0.9 50.83 33.53 1.5 Example 2 81.3 18 0.7 15 25.7 85.8 13.2 0.950.88 33.53 0.6 Example 3 79.3 20 0.7 15 28.6 84.2 14.8 0.9 50.89 33.541.2 Example 4 67.3 32 0.7 15 45.7 74.1 25.0 1.0 50.89 33.55 1.5 Example5 96.8 2 1.2 15 1.7 97.9 0.6 1.5 50.85 33.54 1.2 Example 6 80.8 18 1.215 15.0 85.5 12.9 1.6 50.92 33.54 0.6 Example 7 78.8 20 1.2 15 16.7 83.914.5 1.6 50.92 33.55 1.2 Example 8 66.8 32 1.2 15 26.7 73.7 24.6 1.750.9 33.57 1.4 Example 9 96 2 2 19 1.0 97.5 0.1 2.5 50.89 33.6 1 Example10 96 2 2 110 1.0 97.5 0.1 2.5 50.9 33.61 1.1 Example 11 88 10 2 25 5.091.4 6.0 2.6 50.9 33.6 1 Example 12 80 18 2 45 9.0 85.0 12.3 2.7 50.9433.6 0.6 Example 13 80 18 2 19 9.0 85.0 12.3 2.7 50.94 33.6 0.6 Example14 78 20 2 25 10.0 83.4 13.9 2.7 50.94 33.6 1 Example 15 66 32 2 19 16.073.1 24.1 2.8 50.92 33.59 1.2 Example 16 66 32 2 2 16.0 73.1 24.1 2.850.91 33.59 1.2 Example 17 79 18 3 25 6.0 84.4 11.6 4.0 50.99 33.65 0.6Example 18 77 20 3 25 6.7 82.7 13.2 4.0 50.99 33.67 1 Example 19 65 32 325 10.7 72.4 23.4 4.2 50.95 33.62 1 Example 20 74 18 8 25 2.3 81.1 7.911.0 51 33.71 0.6 Example 21 72 20 8 25 2.5 79.4 9.6 11.1 50.99 33.720.8 Example 22 60 32 8 25 4.0 68.6 19.9 11.5 50.96 33.7 0.9 Example 2372 18 10 25 1.8 79.7 6.4 13.9 51 33.82 0.6 Example 24 70 20 10 25 2.078.0 8.1 14.0 51 33.84 0.8 Example 25 58 32 10 25 3.2 67.1 18.4 14.5 5133.8 0.8 Comparative Example 1 78.8 20 1.2 15 16.7 83.9 0 0.8 — — 2.1Comparative Example 2 78.8 20 1.2 15 16.7 83.9 0 2.5 — — 2.7 ComparativeExample 3 78.8 20 1.2 15 16.7 83.9 0 0.6 — — 4.3

TABLE 3 Arcing Mobility Mobility Frequency (350° C.) (450° C.) Mobility(times) (cm²/Vs) (cm²/Vs) Ratio Example 1 1 30 22 0.73 Example 2 0 32 321.00 Example 3 2 30 30 1.00 Example 4 2 28 26 0.93 Example 5 1 32 220.69 Example 6 0 38 39 1.03 Example 7 2 36 36 1.00 Example 8 2 30 280.93 Example 9 1 30 24 0.80 Example 10 1 28 27 0.96 Example 11 0 32 240.75 Example 12 0 32 34 1.06 Example 13 0 32 33 1.03 Example 14 2 30 311.03 Example 15 2 29 25 0.86 Example 16 2 29 22 0.76 Example 17 0 25 261.04 Example 18 3 24 25 1.04 Example 19 3 22 21 0.95 Example 20 1 19 201.05 Example 21 3 18 19 1.06 Example 22 3 15 14 0.93 Example 23 1 16 161.00 Example 24 3 15 16 1.07 Example 25 3 14 13 0.93 Comparative Example1 6 36 31 0.86 Comparative Example 2 5 36 30 0.83 Comparative Example 310 36 31 0.86

The oxide sintered material of each of Comparative Examples 1, 2 and 3has the same composition (element content rate) as the oxide sinteredmaterial of Example 7, but does not contain the Zn₄In₂O₇ crystal phase(IZ crystal phase). As a result, compared with the semiconductor device(TFT) manufactured using the oxide sintered material of Example 7 as thesputtering target, the field-effect mobility of the semiconductor device(TFT) manufactured using the oxide sintered material of ComparativeExamples 1, 2 and 3 as the sputtering target after the semiconductordevice is subjected to the heat treatment (annealing) in nitrogenatmosphere under the atmospheric pressure at 450° C. for 10 minutes,which is the “mobility (450° C.)” is largely reduced.

Comparing Example 9 and Example 10, Example 12 and Example 13, andExample 15 and Example 16, it is found that these oxide sinteredmaterials have the same contents of In, Zn and W but differ in thecontent of Zr. From the comparison of these Examples, it is understoodthat in order to maintain a high field-effect mobility when annealing ata high temperature, it is preferable to set the Zr content to 2 ppm ormore and less than 100 ppm.

It should be understood that the embodiments disclosed herein have beenpresented for the purpose of illustration and description but notlimited in all aspects. It is intended that the scope of the presentinvention is not limited to the description above but defined by thescope of the claims and encompasses all modifications equivalent inmeaning and scope to the claims.

REFERENCE SIGNS LIST

10, 20, 30: semiconductor device (TFT); 11: substrate; 12: gateelectrode; 13: gate insulating film; 14: oxide semiconductor film; 14 c:channel part; 14 d: drain electrode forming part; 14 s: source electrodeforming part; 15: source electrode; 16: drain electrode; 17: etchstopper layer; 17 a: contact hole; 18: passivation film

The invention claimed is:
 1. An oxide sintered material including anIn₂O₃ crystal phase, a Zn₄In₂O₇ crystal phase and a ZnWO₄ crystal phase,wherein a diffraction angle 2θ at the X-ray diffraction peak derivedfrom the In₂O₃ crystal phase is greater than 50.70° and smaller than51.04°.
 2. The oxide sintered material according to claim 1, wherein thecontent of the In₂O₃ crystal phase is 25 mass % or more and less than 98mass %, and the content of the Zn₄In₂O₇ crystal phase is 1 mass % ormore and less than 50 mass %.
 3. The oxide sintered material accordingto claim 1, wherein the lattice constant of a C-plane of the Zn₄In₂O₇crystal phase is 33.53 Å or more and 34.00 Å or less.
 4. The oxidesintered material according to claim 1, wherein the content of the ZnWO₄crystal phase is 0.1 mass % or more and less than 10 mass %.
 5. Theoxide sintered material according to claim 1, wherein the content oftungsten relative to the total of indium, tungsten and zinc in the oxidesintered material is more than 0.1 atom % and less than 20 atom %, andthe content of zinc relative to the total of indium, tungsten and zincin the oxide sintered material is more than 1.2 atom % and less than 40atom %.
 6. The oxide sintered material according to claim 1, wherein thecontent of zinc relative to the content of tungsten in the oxidesintered material is greater than 1 and less than 80 by atom ratio. 7.The oxide sintered material according to claim 1, further comprisingzirconium, wherein the content of zirconium relative to the total ofindium, tungsten, zinc and zirconium in the oxide sintered material is0.1 ppm or more and 200 ppm or less by atom ratio.
 8. A sputteringtarget comprising the oxide sintered material according to claim
 1. 9. Amethod of manufacturing a semiconductor device including an oxidesemiconductor film, comprising: preparing the sputtering targetaccording to claim 8; and forming the oxide semiconductor film by asputtering method using the sputtering target.
 10. A method of producingan oxide sintered material according to claim 1, comprising: forming theoxide sintered material by sintering a molded body containing indium,tungsten and zinc, forming the oxide sintered material including placingthe molded body at a first constant temperature selected from atemperature range of 500° C. or more and 1000° C. or less for 30 minutesor longer.
 11. The method of producing an oxide sintered materialaccording to claim 10, wherein forming the oxide sintered materialincludes placing the molded body at the first temperature for 30 minutesor longer, and placing the molded body in an oxygen-containingatmosphere at a second temperature which is 800° C. or more and lessthan 1200° C. and higher than the first temperature in this order.
 12. Amethod of producing an oxide sintered material according to claim 1,comprising: preparing a primary mixture of a zinc oxide powder and anindium oxide powder; forming a calcined powder by heat-treating theprimary mixture; preparing a secondary mixture of raw powders includingthe calcined powder; forming a molded body by molding the secondarymixture; and forming the oxide sintered material by sintering the moldedbody, forming the calcined powder including forming a complex oxidepowder including zinc and tungsten as the calcined powder byheat-treating the primary mixture at a temperature of 550° C. or moreand less than 1300° C. in an oxygen-containing atmosphere.
 13. Themethod of producing an oxide sintered material according to claim 12,wherein forming the oxide sintered material includes placing the moldedbody at a first constant temperature selected from a temperature rangeof 500° C. or more and 1000° C. or less for 30 minutes or longer. 14.The method of producing an oxide sintered material according to claim13, forming the oxide sintered material includes placing the molded bodyat the first temperature for 30 minutes or longer, and placing themolded body in an oxygen-containing atmosphere at a second temperaturewhich is selected from a temperature range of 800° C. or more and lessthan 1200° C. and higher than the first temperature in this order.